The Islamic State in Iraq and Syria (ISIS) militant group has come under scrutiny after claiming responsibility for a wave of coordinated attacks in Paris on Nov 13 that left at least 129 people dead and hundreds more wounded.
French investigators believe three cells of the group were involved in the attacks at bars, a concert hall and outside a soccer stadium. ISIS said they carried out the attacks in revenge for French air strikes in Syria and has threatened more violence if France continues its campaign against the group.
Here is what you need to know about the group.
What is ISIS?
The militant group is also known by its other names Islamic State (IS), Islamic State in Iraq and the Levant (ISIL) and its Arabic acronym Daesh.
ISIS first seized the world's attention in June 2014 when it declared the establishment of a caliphate - or an Islamic religious state - that spanned parts of northern and western Iraq and eastern Syria.
Its leader is Abu Bakr Al-Baghdadi, who was born in the Iraqi city of Samarra in 1971 and claims to be a direct descendant of Prophet Mohammed. He was named its Caliph or the head of the state.
After declaring a caliphate, the group laid out edicts spelling out harsh terms of Islamic law under which they would govern. Human rights activists and analysts say the group uses brutal punishments in areas where it is present to control the local population through coercion and fear.
As of June this year, the group is said to control some 300,000 sq km of territory across Iraq and Syria. Within those territories, ISIS has also set up religious schools for children, organised training sessions for new imams and preachers as well as established a consumer protection bureau, according to The Atlantic.
How did it first emerge?
ISIS has its roots in an insurgent group set up by Baghdadi to fight coalition troops following the US-led invasion of Iraq in 2003.
In 2006, Abu Musab Al-Zarqawi, a Jordanian and convicted thief who travelled to Afghanistan to fight the Soviets, created an umbrella organisation of Sunni insurgent groups led by his Al Qaeda in Iraq group. Baghdadi's cell was among the first to join.
When Zarqawi died in a US airstrike that same year, he was succeeded as leader of the umbrella group by Abu Ayoub Al-Masri, an Egyptian who announced the formation of the Islamic State of Iraq. Baghdadi then became its head of religious affairs. In May 2010, Baghdadi became the group's leader following Masri's death in a joint US-Iraqi raid.
In the years since, Baghdadi sought to position himself as the defender of Iraq's disenfranchised Sunni minority while taking advantage of the uprisings in Syria to send his fighters there. The group also renamed itself ISIS from the Islamic State of Iraq.
By early 2014, Baghdadi's forces had swept into the Iraqi cities of Ramadi and Fallujah and controlled wide regions of Syria, including the city of Raqqa which became its de facto capital.
Although its ruthless tactics alienated other rebel groups, ISIS gained many new fighters and valuable battle experience. It also launched strategic attacks to seize resources such as arms caches, oil wells and granaries in Syria.
In June 2014, the group grabbed headlines when it made a sweeping advance in Iraq, seizing Iraq's second city Mosul and swathes of Iraqi territory. The group declared itself a caliphate, with Baghdadi appearing in a video soon after, proclaiming himself caliph and calling on Muslims to help build an empire.
How many members does ISIS have?
While the group's brutal tactics have led even the Syrian rebel movement and the Al Qaeda militant group to officially distance themselves, it remains a threat to governments worldwide and draws a large number of fighters from abroad.
A United Nations report in April 2015 said that some 20,000 foreign fighters from over 100 countries - including Libya, Egypt, Saudi Arabia, Tunisia, Yemen and Pakistan - have travelled to join the militant groups fighting in Iraq and Syria, most of these flowing to ISIS. In Southeast Asia, up to 30 groups in Indonesia, Malaysia and the Philippines have pledged support or had members who pledge support to ISIS. In Singapore, at least seven Singaporeans are known to have been influenced by ISIS, with two of them still believed to be in ISIS territory.
Who are its prominent members?
Baghdadi has galvanised militants from around the world, encouraged by his military successes and plans to redraw the map of the Middle East to create a self-sustaining caliphate. His successes has prompted the US to re-engage in Iraq with air strikes against his fighters three years after pulling out following a long, costly occupation.
Another prominent member is Mohammed Emwazi, whose masked figure appeared in a string of graphic beheading videos released by the group. The 27-year-old Briton, who became known as "Jihadi John", sparked worldwide revulsion with his grisly executions of foreign aid workers and journalists in Syria on camera. He was reported to have died in a US drone strike in Syria on Nov 12.
How is the group funded?
There is no credible estimate of the secretive group's net worth, but the group is believed to be one of the best-financed terrorist organisations in the world, according to a January report in The Economist. Terror experts say that unlike other groups which receive money from foreign fighters, ISIS largely funds itself. The majority of the group's money comes from oil sales to local traders from wells under its control.
A Reuters report last year also said the group had formalised a system of internal financing that includes an Islamic form of taxation and looting to run their "state" effectively. According to the report, the group collects money from small merchants, petrol station owners, generator owners, small factories, big companies and even pharmacists and doctors.
Like many militant groups, the group also counts kidnapping as a funding source. The Economist report said ISIS earned at least US$20 million (S$28 million) last year from ransoms paid for hostages.
What recent attacks have ISIS conducted?
Recent major attacks
There have been several major attacks linked to ISIS this year.
* France: In January this year, France was also shaken by a series of deadly attacks by Islamist militants with links to ISIS that included the killing of 12 people at the office of the satirical weekly Charlie Hebdo.
* Tunisia: In June this year, 38 foreign tourists were killed in a beach attack in Tunisia, while 21 tourists were killed at a museum by gunmen in March. ISIS claimed responsibility for both attacks.
* Lebanon: More recently were the twin suicide bombings last Thursday (Nov 12) in Beirut which killed 44 people. The bombings targeted a crowded residential district in Beirut's southern suburbs, a stronghold of the Shi'ite Muslim group Hezbollah, which is fighting ISIS in Syria.
* Egypt: The Paris attacks also came more than two weeks after the militants claimed responsibility for bringing down a Russian airliner over Egypt's Sinai Peninsula on Oct 31, killing all 224 people on board. ISIS said it was done in retaliation over the Russian air strikes in Syria.
* Turkey: The violence in Paris also comes just over a month after two suspected ISIS suicide bombers blew themselves up in Ankara, killing more than 100 people in Turkey's worst such attack. Turkey had stepped up its fight against the militants since July, when it began launching air strikes against the group and opened its air bases to US-led coalition war planes.
In addition, ISIS has also beheaded local and foreigners in Syria, including enemy combatants, aid workers and journalists as well as people it has deemed as violating its hardline interpretation of Islamic law.
It has released many hostage execution videos to threaten the West and admonish its Arab allies for targeting the group. Those executed have included US journalists Steven Sotloff and James Foley, US aid worker Abdul-Rahman Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto, among others.
What is the global response to ISIS?
In Sept 2014, the US began leading an international coalition in Syria to conduct air strikes on ISIS militants and other extremist groups there. Countries backing the US include Australia, Britain, Belgium, Canada, Denmark, France, Jordan, Netherlands, Bahrain, Saudi Arabia, Turkey and the United Arab Emirates.
Russia began its own air campaign in Syria in October. But Moscow's critics say it has been targeting mainly areas controlled by other groups opposed to its ally, President Bashar al-Assad.
Following the Paris attacks, the Obama administration vowed to intensify military coordination and intelligence sharing as part of its battle against the group. That, however, has not stopped the scrutiny of the US strategy against ISIS in Washington - even from within Obama's Democrats. Prominent Democrat Adam Schiff on Sunday (Nov 15) called the strategy a failure that could lead to more attacks while Republican awmakers have dismissed the air campaign as "pinpricks" that do not add up to a comprehensive strategy.
SOURCE: AGENCE FRANCE-PRESSE, REUTERS, BLOOMBERG, BBC, THE ECONOMIST, NEW YORK TIMES, THE ATLANTIC