The United States wants to bolster a coalition fighting Islamic State in northeastern Syria, a senior State Department official said after the leader of the jihadi movement, Abu Bakr al-Baghdadi, was killed in a weekend operation.

World leaders welcomed Abu Bakr's death, but they and security experts warned that the group which carried out atrocities against religious minorities and horrified most Muslims remained a security threat in Syria and beyond.

The official said that President Donald Trump, by announcing the withdrawal of US forces from northern Syria on Oct 6, did not suggest that Washington was abandoning the fight against Islamic State.

"There was never an idea that we would abandon the mission of going after Isis... This is a major effort that is continuing," the official told reporters yesterday.

Foreign ministers will meet in Washington on Nov. 14 to discuss the mission.

Trump has softened his pullout plans for Syria after a backlash from Congress, including fellow Republicans, who say he enabled a long-threatened Turkish incursion on Oct 9 against Kurdish forces in Syria who had been America's top allies in the battle against Islamic State since 2014.

US special forces carried out the Syrian operation in which Abu Bakr killed himself and three of his children by detonating a suicide vest when he was cornered in a tunnel.

Trump said yesterday that he may declassify and release part of the video taken last Saturday of the raid. The video is believed to include aerial footage and possibly footage from cameras mounted on the soldiers who stormed Abu Bakr's compound.

"We're thinking about it. We may," Trump told reporters before flying to Chicago. "We may take certain parts of it and release it."

Trump said on Sunday that Baghdadi had died "whimpering and crying" in a raid that fulfilled his top national security goal.

'Lone wolf' threat

Kremlin spokesman Dmitry Peskov declined to say if the United States had told Russia about the operation in advance.

But he added: "If this information is confirmed we can talk about a serious contribution by the president of the United States to the fight against international terrorism."

French President Emmanuel Macron (photo) said Abu Bakr's death was a major blow against Islamic State but "the fight continues to finally defeat this terrorist organisation".

British Prime Minister Boris Johnson said: "We will work with our coalition partners to bring an end to the murderous, barbaric activities of Daesh (Islamic State) once and for all."

Australian Prime Minister Scott Morrison told reporters: "This is a many-headed monster... As you cut one off, another one inevitably arises."

In Southeast Asia, an important focus for Islamic State, officials said security forces were preparing for a long battle to thwart the group's ideology.

The Philippines, Indonesia and Malaysia, home to some of Asia's most organised Islamist militants, said they were braced for retaliation by Islamic State loyalists, including "lone wolf" attacks by radicalised locals.

Capable and dangerous

Though Abu Bakr's death will unsettle Islamic State, it remains capable and dangerous, said Delfin Lorenzana, defence secretary of the Philippines, where the group's influence has taken hold in its troubled Mindanao region.

"This is a blow to the organisation, considering Abu Bakr's stature as a leader. But this is just a momentary setback considering the depth and reach of the organisation worldwide," Lorenzana said. "Somebody will take his place."

Islamic State has no declared successor as leader. But the group has in the past proved resilient, continuing to mount or inspire attacks in the region and beyond despite losing most of its territory in recent years.

Abu Bakr had long been sought by the United States - which offered a US$25 million (RM104.65 million) reward - as leader of a jihadist group that at one point controlled large areas of Syria and Iraq, where it declared a caliphate.

Islamic State has brutally attacked religious minorities and launched deadly strikes on five continents in a violent campaign that horrified most Muslims.

In their long hunt for Abu Bakr, Iraqi intelligence teams secured a break in February 2018 after one of his top aides gave them information on how he escaped capture for so many years, two Iraqi security officials said.

Abu Bakr held strategy talks with his commanders in moving minibuses packed with vegetables in order to avoid detection, Ismael al-Ethawi told officials after he was arrested by Turkish authorities and handed to the Iraqis.

"Ethawi gave valuable information which helped the Iraqi multi-security agencies team complete the missing pieces of the puzzle of Abu Bakr's movements and places he used to hide," one of the Iraqi security officials said.

Iraqi security officials said Kurdish intelligence agents had exchanged information with counterparts in Baghdad on the movements of Abu Bakr and his aides in Syria. One of the Kurds' sources passed on a "golden tip" earlier this year.

Suspicious movements were spotted by locals at a house in a village in Syria, which was placed under surveillance and turned out to be the house used by Abu Bakr, the Iraqi officials said.

US pullback

The raid on Abu Bakr comes weeks after Trump announced the withdrawal of US troops from northeastern Syria.

Critics expressed concern at the abandoning of the Kurdish fighters who were instrumental in defeating Islamic State in Syria, and said the move might allow the group to regain strength and pose a threat to US interests.

Trump (photo) said the raid would not change his decision to withdraw troops from Syria.

But killing Abu Bakr could help blunt those concerns, as well as boosting Trump domestically at a time when he is facing an impeachment inquiry in the US House of Representatives.

Egypt, which is fighting militants loyal to Islamic State, said the killing of Abu Bakr is "an important step towards eradicating terrorism".

US foe Iran, which accuses the United States and its allies of creating Islamic State, was dismissive. Information Minister Mohammad Javad Azari-Jahromi, tweeted: "Not a big deal, You just killed your creature."

Night-time raid

In the hours before Trump's announcement, sources in the region had described the raid on a compound in the village of Barisha, in Idlib province bordering Turkey, in the early hours of Sunday.

Trump said eight helicopters carried US special forces to Abu Bakr's compound, where they were met with gunfire before blasting their way in.

The president said he watched the operation in the Situation Room of the White House.

At the height of its power, the Islamic State ruled over millions of people from northern Syria to the outskirts of Baghdad.

Thousands of civilians were killed by the group as it mounted what the United Nations called a genocidal campaign against Iraq's Yazidi minority. It also caused worldwide revulsion by beheading foreign nationals from several countries, including the United States, Britain and Japan.

The group has claimed responsibility for or inspired attacks in cities including Paris, Nice, Orlando, Manchester, London and Berlin, and in Turkey, Iran, Saudi Arabia and Egypt.

- Reuters