Profile: Islamic State in Iraq and the Levant (ISIS)
The Islamic State in Iraq and the Levant (ISIS) is a jihadist group active in Iraq and Syria.
ISIS was formed in April 2013 and grew out of al-Qaeda's affiliate organisation in Iraq. It has since become one of the main jihadist groups fighting government forces in Syria.
The final "s" in the acronym Isis stems from the Arabic word "al-Sham". This can mean the Levant, Syria or even Damascus but in the context of the global jihad it refers to the Levant.
Its precise size is unknown, but it is thought to include thousands of fighters, including many foreign jihadists.
Analysts say non-Syrians constitute a majority of Isis's elite fighter corps and are disproportionately represented in its leadership.
It took over the city of Raqqa after rebels overran the city in March 2013. It was the first provincial capital to fall under rebel control.
It also has a presence in a number of towns close to the Turkish border in the north of the country, and has gained a reputation for brutal rule in the areas that it controls.Inter-rebel tension
The group has been operating independently of other jihadist groups such as the Nusra Front and has had a tense relationship with other rebels in Syria.
In July, a commander of the Western-backed Free Syrian Army (FSA) was reportedly shot dead by Isis fighters in the coastal province of Lattakia.
There were also reports of deadly clashes between the two groups in the north-western province of Idlib. Isis also seized the northern town of Azaz from the FSA on 18 September.
There has also been friction with other Islamists. In November 2013, ISIS was accused of killing a prominent member of the Syrian Islamist rebel group Ahrar al-Sham.
In the most recent sign of continuing tension, ISIS suffered losses in two days of fighting against an alliance of other rebel forces in Aleppo and Idlib provinces.Isis strongholds in rebel-held and contested areas Iraq violence
Isis originated in Iraq and continues to be active there too.
When the group was formed in April 2013, it was initially presented as a merger between the al-Qaeda-affiliated Islamic State of Iraq (ISI) and the Syrian jihadist rebel group, the Nusra Front.
However, the announcement of the merger by ISI leader Abu Bakr al-Baghdadi was immediately rejected by the Nusra Front.
Two months later, al-Qaeda leader Ayman Zawahiri reportedly ordered the merger to be annulled.
In August 2013, ISIS claimed responsibility for a series of bomb attacks in Baghdad and other areas of Iraq in which dozens were killed.
And in early January it capitalised on growing tension between Iraq's Sunni minority and Shia-led government by seizing control of parts of the western Sunni town of Fallujah.
It was also reported to be involved in clashes with security forces in the town of Ramadi, which like Fallujah is in Anbar province, a centre of Sunni militant activity.
There are indications that the war in Syria may be worsening tensions in Iraq.
An adviser to the Prime Minister, Saad al-Mutalabi, has told the BBC that insurgents had smuggled weapons into Fallujah from Syria.
"Because of what is happening in Syria and the new ammunition and missiles they received from Saudi Arabia into Syria, they managed to smuggle quite a vast quantity of equipment to fight the Iraqi people," Mr Mutalabi said.