A blast at the headquarters of the National Security Bureau (NSB) in Damascus on 18 July killed President Bashar al-Assad's brother-in-law and Deputy Defence Minister Gen Assef Shawkat, Defence Minister Gen Daoud Rajiha, former Defence Minister Hassan Turkomani and NSB chief Hisham Ikhtiar. Here are their profiles:
Assef Shawkat, deputy defence minister
Gen Shawkat was considered one of the president's top security chiefs.
However, he was replaced in 2010 as head of Military Intelligence and made deputy chief-of-staff of the armed forces and deputy defence minister. Although he appeared to have been promoted, opposition figures said he was seen to have been at fault in the 2008 assassination of Hezbollah military commander Imad Mughniyeh in an area of Damascus that fell under his responsibility.
Analysts disagreed, however, saying there was no political significance and that preparations were in fact being made to appoint Gen Shawkat chief-of-staff of the armed forces or defence minister.
Born in 1950 to a middle-class Alawite family in Tartus, he studied law at Damascus University. He joined the army in the late 1970s.
He rose through the ranks, but his fortunes changed spectacularly in the mid-1990s when he married Hafez al-Assad's only daughter, Bushra - despite misgivings from within the Assad family because he was a divorced father-of-five who was 10 years her senior. They eloped after the death of Basil Assad, who had objected to the match.
After receiving the blessing of Hafez, he was welcomed into the family and built a close relationship with Bashar. Bushra reportedly nurtured the relationship through her influential role as the president's secretary.
Former Vice-President Abdul Halim Khaddam said Gen Shawkat was a "smart, cultivated, and courageous officer with great ambitions", who had established ties with intelligence chiefs and other powerbrokers.
But there were reports of friction with Bashar's younger brother, Maher, who is alleged to have shot him in the stomach in 1999. He was allegedly flown to Paris for treatment at a military hospital.
Gen Shawkat later became the de facto chief of military intelligence, a title he officially acquired in 2005.
After the 11 September 2001 attacks, Gen Shawkat was one of the president's main liaisons to intelligence agencies in the US and Europe and helped set up a US intelligence operation in Syria, which was later shut down after relations between the two countries soured.
In 2005, Maher and Shawkat were both mentioned in a preliminary report by UN investigators as one of the people who might have planned the assassination of the former Lebanese Prime Minister, Rafik Hariri.
The next year, Gen Shawkat was named a Specially Designated National (SDN) by the US, allowing his assets to be frozen. It said he had "been a key architect of Syria's domination of Lebanon, as well as a fundamental contributor to Syria's long-standing policy to foment terrorism".
The US and EU imposed sanctions on Gen Shawkat in 2011, accusing him of playing a key role in suppressing demonstrations. In January 2012, he was reported to have been involved in negotiations which led to an unprecedented truce between security forces and the rebel Free Syrian Army (FSA) in Zabadani, a mountain town north-west of Damascus. The truce lasted just under a month, after which the military recaptured it.
In mid-May 2012, opposition activists claimed that Gen Shawkat had died and been buried in his hometown of Madhala after being poisoned by rebels. Interior Minister Mohammed al-Shaar, Defence Minister Daoud Rajiha, National Security Bureau (NSB) chief Hisham Ikhtiar and Hassan Turkomani, assistant to the vice-president, were also allegedly killed. Gen Turkomani subsequently appeared on TV to dismiss the report, while Mr Shaar denied them in a telephone interview, but Gen Shawkat did not do so, fuelling the rumours about his death.
On 18 July, state media reported that Gen Shawkat had been killed in a suicide bomb attack at the headquarters of the National Security Bureau.
Daoud Rajiha, defence minister
Gen Daoud Rajiha was appointed defence minister in August 2011, and remained in the post after a cabinet reshuffle in June.
The 65 year old had previously served as chief of staff of the armed forces for seven years. He was promoted to the rank of general in 2005.
He specialised in artillery at the Syrian military academy, from which he graduated in 1967.
It is believed Gen Rajiha was a Greek Orthodox Christian, a rarity in the Syrian military and government, which is dominated by the Alawite sect of President Bashar al-Assad.
In March 2012, the US Treasury imposed sanctions on Gen Rajiha for his role in the repression of dissent in Syria. The EU also added him to its list of designated officials, saying he was responsible for the military's involvement in the crackdown on protesters.
Hassan Turkomani, assistant to the vice-president
Gen Hassan Turkomani was appointed assistant to the vice-president - with the rank of minister - in 2009. He was also said to been made a special envoy of President Assad.
Born in 1935, Mr Turkomani joined the army in the 1950s. He fought against Israel and in Lebanon, before being made a general in the 1980s and military chief of staff in 2002.
His appointment as defence minister in 2004 - replacing Mustafa Tlas, who had been in that position for 32 years - went against speculation that the next postholder would be a civilian.
A Sunni Muslim unlike many in the Syrian elite, Gen Turkomani was also a long-standing senior member of the ruling Baath Party, serving on its Regional Command and Central Committee.
Activists say that after protests erupted against President Assad in 2011, Gen Turkomani was appointed head of the security forces' crisis management office, which is based at the National Security Bureau's headquarters in Damascus. In August, the EU imposed sanctions on the general as it targeted senior government officials.
Hisham Ikhtiar, director of the National Security Bureau (NSB)
Born in 1941, Gen Ikhtiar was the head of the Baath Party Regional Command's National Security Bureau (NSB), which co-ordinates the work of Syria's intelligence agencies and formulates recommendations for the president. Between 2001 and 2005, he was in charge of the General Security Directorate (GSD).
In 2006, the US imposed financial sanctions on Gen Ikhtiar for "significantly contributing to the Syrian government's support for designated terrorist organisations", including Hezbollah. While at the GSD, Gen Ikhtiar directed activities that "significantly contributed to the Syrian government's military and security presence in Lebanon", it said. In 2007, he was included on a list of Syrians forbidden to enter US soil.
Gen Ikhtiar was reportedly charged with quelling the initial pro-democracy protests in Deraa. The brutal crackdown launched by the security services in the southern city helped trigger the recent nationwide unrest.
In May 2011, the US treasury department imposed sanctions on the National Security Bureau, saying it had directed Syrian security forces to use extreme force against demonstrators. The EU and US later imposed individual sanctions on Gen Ikhtiar, with the latter saying he had directed security forces to "use extreme force against demonstrators".