Key questions and answers about the Islamic State group that beheaded two American journalists and a British aid worker, and which US President Barack Obama described as a "cancer".
Q. What is the Islamic State group?
A. It emerged in Iraq in 2006, three years after the US-led invasion, spurred by global terror network Al-Qaeda. Initially known as the Islamic State in Iraq.
The jihadists launched deadly attacks on the Shiite majority, oppressed under toppled Sunni dictator Saddam Hussein, and American troops. Sunni tribes rose up against them.
Jihadists rallied to the rebellion in neighbouring Syria in July 2011, at first joining forces with the Al-Nusra Front, Al-Qaeda's Syria franchise, battling to topple the regime.
In April 2013, they announced the creation of the Islamic State of Iraq and the Levant (ISIL), and within months the group began to establish full control over areas that had fallen into rebel hands by driving out its competitors.
In January, deadly clashes erupted between ISIL and Al-Nusra and other rebel groups which refused to fight under the jihadists' banner and instead accused them of atrocities.
In June, ISIL declared an Islamic caliphate in territory it controls in northern Syria and Iraq, renamed itself the Islamic State (IS) and ordered Muslims to obey its leader, Abu Bakr al-Baghdadi.
Unlike other groups battling Syria's regime, members of IS consider themselves to be running a state, complete with judicial, military, educational, diplomatic and financial institutions that they say follow Islamic law.
Q. How many fighters does IS have?
A. There are no precise figures, but the Central Intelligence Agency says IS militants in Iraq and Syria now have about 20,000 to 31,500 fighters on the ground.
The Syrian Observatory for Human Rights monitoring group says IS actually has more than 50,000 fighters in Syria alone, including 20,000 jihadists from Chechnya, Europe, China and Gulf Arab countries.
IS recruits through social networks, but jihadists have also joined the group locally out of fear or lured by attractive salaries.
Many IS commanders in both Iraq and Syria are ex-members of Saddam Hussein's army and are skilled fighters.
Q. How much land does IS control?
A. In Syria it controls about 25 percent of the country or 45,000 square kilometres (18,000 square miles) of territory, while in Iraq it holds sway over 170,000 square kilometres, or 40 percent of the country. Most of this land is desert.
Syria expert Fabrice Balanche says the total amount of territory the IS holds in Syria and Iraq is just under the size of Britain.
In Syria, the "caliphate" announced in June spreads from Manbaj in the northern province of Aleppo, across the northeastern provinces of Raqa and Hasakeh to the eastern oil-rich province of Deir Ezzor and to the Albu Kamal border town with Iraq.
In Iraq, it controls Sunni regions in the north and west, including the second biggest city of Mosul.
Q. How does it lure foreign jihadists?
A: IS has bewitched Western jihadists through the use of spectacular "Hollywood-style" demonstrations of force -- brutal beheadings and a swift land-grab -- says Lebanese writer Hazem al-Amin. Other experts say IS's brand of fundamentalist Islam has attracted followers especially among the disenchanted.
Q. How is it financed?
A. Experts say that through a combination of racketeering, kidnapping for ransom and other criminal activity, as well as donations from wealthy private individuals in the Gulf, the group has built up a financial war chest that is the envy of militant organisations the world over.
Germany's development aid minister Gerd Mueller has accused energy-rich Qatar of financing the jihadists. But Romain Caillet, an expert on Islamists, says funding from the Gulf represents only five percent of its income.
The jihadists smuggle and sell large quantities of oil extracted from areas of Iraq and Syria under their control, as well as stolen antiquities.
In their June offensive on Mosul, the jihadists emptied out the coffers of the city's banks, containing some $400 million.
Q. How does it treat people under its control?
A. While it does provide some social services to people living under its rule, IS has become known for its brutal reign of terror -- crucifixion, beheading and flagellation have all been used by the group against its enemies. Women accused of adultery face death by stoning.
Q. What does the future hold for IS?
A. Caillet believes its key goal is to consolidate the "caliphate", but others, such as Amin, believe that the group is bound to crumble and be forced underground following tough Western strikes.