Boris Johnson tweeted the death of Baghdadi is an important moment in the fight against terror (File)
British Prime Minister Boris Johnson on Sunday hailed the death of ISIS founder Abu Bakr al-Baghdadi as "an important moment" but said the fight against his group "is not yet over".
"The death of Baghdadi is an important moment in our fight against terror but the battle against the evil of Daesh is not yet over," he wrote on Twitter.
"We will work with our coalition partners to bring an end to the murderous, barbaric activities of Daesh once and for all."
Defence Secretary Ben Wallace said the ISIS group's leaders "have twisted Islam to groom thousands of people into joining their evil cause".
"I welcome the action that has been taken. The world will not miss Al-Baghdadi," he tweeted.
US President Donald Trump on Sunday said that elusive ISIS leader Abu Bakr al-Baghdadi was killed, dying "like a dog," in a daring, nighttime raid by US special forces deep in northwest Syria.
Mr Trump told the nation in a televised address from the White House that US forces killed a "large number" of ISIS terrorists during the raid which culminated in cornering Baghdadi in a tunnel, where he set off a suicide vest.
"He ignited his vest, killing himself," Mr Trump said.
"He died after running into a dead end tunnel, whimpering and crying and screaming all the way," Mr Trump said, adding that three of Baghdadi's children also died in the blast.
Mr Trump said that the raid -- which required flying more than an hour by helicopter in both directions from an undisclosed base -- had been accomplished by help from Russia, Syria, Turkey and Iraq.
Special forces "executed a dangerous and daring nightime raid in northwestern Syria and accomplished their mission in grand style."
At its height, ISIS controlled swaths of Iraq and Syria in a self-declared state known as a caliphate, characterized by the brutal imposition of a puritanical version of Islam.
In addition to oppressing the people it governed, ISIS planned or inspired terrorism attacks across Europe, while using expertise in social media to lure large numbers of foreign volunteers.
It took years of war, in which ISIS became notorious for mass executions and sickening hostage murders, before the caliphate's final slice of territory in Syria was seized this March.
The death of Baghdadi comes as a big boost for Mr Trump, whose abrupt decision to withdraw a small but effective deployment of US forces from Syria caused fears that it would give ISIS remnants and sleeper cells a chance to regroup.