Almost every day of the uprising against the rule of Syrian President Bashar al-Assad has brought new reports of shootings, deaths and injuries.
Reports are hard to verify, as few journalists are allowed into Syria and casualty numbers come primarily from government and opposition sources. But there have been some major attacks that stand out as particularly violent episodes in an already bloody conflict.
Deraa/Damascus, 22 April 2011
The Syrian uprising, then a month old, experienced its bloodiest day until then on 22 April when 72 protesters were killed by security forces firing on crowds.
Many of the dead were in the southern village of Ezra, near Deraa and in a suburb of Damascus.
Jisr al-Shughour, 3-6 June 2011
In June 2011, the Syrian government announced that 120 security personnel had been killed in the north-western town of Jisr al-Shughour.
The figure may have been inflated but it was a major attack and, as the BBC's correspondent Jim Muir said at the time, it showed that the government was facing an armed uprising rather than mass peaceful protests.
Opposition groups initially denied they were behind the killings, but later investigations suggested that when protesters were fired on during a funeral, they attacked the state security forces. Some soldiers may also have been killed when they refused to shoot demonstrators.
Afterwards, thousands of residents fled Jisr al-Shughour fearing retribution from the army.
Jabal al-Zawiya, 19-20 December 2011
Villages in the area of Jabal al-Zawiya in Idlib province were the site of a massacre of army defectors in December last year.
Opposition activists said about 70 soldiers were mown down by machine-guns on 19 December after hundreds fled their positions between the villages of Kafrouaid and Kansafra. This was later backed up by eyewitnesses and a report by Human Rights Watch.
The London-based Syrian Observatory for Human Rights said a further 111 people - also mostly army defectors - were hunted down by the army and killed the next day in an "organised massacre".
Homs, 3 February 2012
Syrian forces began shelling the restive city of Homs on 3 February, in what was to become a month-long bombardment.
Early reports talked of as many as 200 deaths, but one of the main activist groups later revised its confirmed number down to 55.
The BBC's Paul Wood, who was in Homs travelling with fighters from the Free Syrian Army, described a city under siege.
Homs, 12 March 2012
The bodies of 45 people, mostly women and children, were found in the Karm el-Zeytoun neighbourhood of Homs on 12 March.
Most had had their throats cut or had stab wounds, while others had reportedly been burned with heating oil and had their limbs broken.
Opposition activists and human rights groups said they had been killed by pro-government militiamen, the shabiha, who had entered the area after heavy government shelling.
Syrian state news blamed "armed terrorist gangs" for the killings, saying they had kidnapped residents of Homs, killed them and then filmed the bodies to discredit Syrian forces.
Taftanaz, 3 April 2012
Syrian forces entered Taftanaz in Idlib province. For two days, the army used helicopters and tanks to attack the town with shells and artillery.
The BBC's Ian Pannell said Taftanaz now had two mass graves, holding approximately 57 people.
The attack on the town was part of a major Syrian army offensive in the area at the time, documented by Human Rights Watch in its report They Burned My Heart.
Houla, 25 May 2012
In May 2012, residents of Taldou, near the town of Houla in Homs province, said pro-government shabiha militiamen had been sent into their village. They said it came after the Syrian army unleashed a barrage of heavy weapons in response to a local anti-government demonstration.
The UN Office of the High Commissioner for Human Rights (OHCHR) said most of the 108 victims, including 49 children and 34 women, had been shot in their homes. No more than 20 had been killed by the tank and artillery fire which preceded the raid, it added.
The government, however, denied all responsibility, saying its soldiers had been attacked and that armed terrorists had killed the civilians.
On 15 August 2012, a report by the UN Independent International Commission of Inquiry (CoI) on Syria concluded that there were reasonable grounds to believe that government forces and shabiha were responsible for the killings of civilians at Houla, which had been "deliberate and connected to the ongoing armed conflict".
It said the government had failed to investigate the incident, and found that "the elements of the war crime of murder have been met".
Hama, 6 June 2012
At least 78 people, many of them women and children, were killed in a single village in the central Hama province, according to activists. Most of those who died had been stabbed and shot.
According to activists, government-backed militia were behind the deaths in the village of Qubair.
The government, meanwhile, said that a "terrorist group" carried out the killings and claims that only nine people died.
Tremseh, 12 July 2012
There are conflicting reports about the killing of between 39 and 220 people in Tremseh, a village in Hama province.
Observers from the UN Stabilisation Mission in Syria (UNSMIS) reached the area on 14 July and documented evidence of a heavy bombardment by government forces.
They found that 50 houses had been burned or destroyed, and said "pools of blood and brain matter were observed in a number of homes".
The "consistent account" relayed by 27 villagers who were interviewed by the UN team indicated that the attack began in the early hours of 12 July with the shelling of the village followed by a ground assault.
UNSMIS said it appeared the attack was "targeted at army defectors and activists", and confirmed the use of direct and indirect weapons, including artillery, mortars and small arms. They said the death toll was unclear.
The Syrian government said at least 50 people were killed in Tremseh, but it blamed "armed terrorist groups".
Darayya, late August 2012
Witnesses and activists said on 25 August 2012 that more than 300 people, including women and children, had been killed by government forces as they stormed Darayya, a south-western suburb of Damascus.
Residents described how troops first closed off the town, preventing civilians from fleeing, then shelled it intensively for several days before carrying out house-to-house searches which ended in executions.
The Local Co-ordination Committees (LCC), an activist network, said on 25 August that at least 633 people had died in Darayya since the bombardment began on 22 August, including 300 it alleged had been executed.
Video footage and photographs posted online by activists purportedly showed five mass graves; others dozens of bodies piled in a mosque.
Witnesses said government forces had killed civilians, including whole families, in cold blood, shooting them at close range or using knives.
State media blamed the opposition for the killings and reported that Darayya had been "cleansed of terrorist remnants".
Halfaya, 23 December 2012
Opposition activists said on 23 December that 90 people had been killed during a government air strike as they were queuing at a bakery in Halfaya, in central Hama province.
Dozens more people were reportedly injured, although there was no independent confirmation of the numbers.
Activists posted videos online which purported to show the aftermath of the attack, with bodies strewn on a road and some buried under the rubble of a building.
Syrian state TV broadcast a news flash saying that an "armed terrorist group" had carried out an attack, then filmed it in order to blame it on the Syrian army. It did not specify the method of attack.
Haswiya, 15 January 2013
As usual, government officials and activists gave differing accounts of how some 100 people were killed in the village of Haswiya, outside Homs, on 15 January 2013.
The BBC later visited the site to assess the evidence.
Syrian security forces who escorted the BBC team blamed the Islamist al-Nusra Front, a militant group fighting alongside the rebels. The Front was seeking revenge against the villagers for supporting the government, they said.
But activists blamed the pro-government shabiha. One woman told the BBC how government troops stood by as the militiamen carried out the killings.
A number of sources concurred that security forces had entered Haswiya at about midday, blocking off exit routes and making arrests, and then left before gunmen arrived and carried out the killings.
A forensic pathologist told the BBC that footage appeared to show that most of the victims had been shot before their homes were burnt.
Jdaidet al-Fadl, April 2013
The Syrian army stormed the town of Jdaidet al-Fadl, near Damascus, killing at least 80 people, opposition activists said.
The attack followed five days of heavy fighting.
Some reports put the death toll much higher.
Al-Bayda and Baniyas, 2-3 May 2013
Opposition activists say more than 200 men, women and children were killed in what they said was a brutal sectarian attack and one of the worst massacres of the war.
A Human Rights Watch (HRW) report published in September supported this claim, saying at least 248 people were killed in mass executions by government forces.
The government, however, says it killed 40 "terrorist fighters" during an operation in the two towns in Tartous province on Syria's Mediterranean coast.
What provoked the military assault is disputed, but both sides seem to agree that government troops had been ambushed by rebel fighters earlier on 2 May.
Families huddled together as regular troops, backed by the paramilitary National Defence Force (NDF), entered the village of al-Bayda later that day. The following day they attacked neighbouring Baniyas.
Based on interviews with survivors and video evidence, HRW found that "the overwhelming majority" were executed after the military clashes had ended and the opposition fighters had retreated.
"The (government) forces entered homes, separated men from women, rounded up the men of each neighbourhood in one spot, and executed them by shooting them at close range," the report said.
At least 23 women and 14 children, including infants, were among those executed, it added.
Hatla, June 2013
Rebels attacked the village of Hatla in eastern Syria, killing at least 60 Shia Muslim residents, most of them pro-government fighters, according to the Syrian Observatory for Human Rights.
Khan al-Assal, 22-23 July 2013
Rebels captured the northern town of Khan al-Assal, allegedly killing 150 government soldiers.
The Syrian Observatory for Human Rights said 51 of the dead had been summarily killed.
Alawite villages, 4 August 2013
Rebels carrying out a military offensive near Latakia killed as many as 190 civilians, according to Human Rights Watch.
The group said its findings "strongly suggest" crimes against humanity were committed in the Alawite villages of Barouda, Nbeiteh, al-Hamboushieh, Blouta, Abu Makkeh, Beyt Shakouhi, Aramo, Bremseh, Esterbeh, Obeen and Kharata.
Ghouta, 21 August 2013
Activists believe that more than 500 people lost their lives in ant attack on the Ghouta agricultural belt around Damascus.
Numerous videos showing large numbers of distressed and visibly sick adults and children with no external signs of injury were uploaded to the internet.
UN chemical weapons inspectors confirmed that the nerve agent sarin was used.