The UK will continue to attack Islamic State until its "poisonous global network" is destroyed, Defence Secretary Gavin Williamson said.
At a summit in Rome, Mr Williamson told allies that the UK will not be complacent in confronting terrorism and IS remained "hell bent" on directing and inspiring attacks at home and abroad.
The Royal Air Force has struck IS targets 22 times in the past three weeks, the Ministry of Defence said.
Mr Williamson's comments came as the fate of two British men suspected of being members of an Islamic State execution group dubbed "The Beatles" risked becoming a diplomatic row between the UK and United States.
Mr Williamson said: "The UK will not be complacent when it comes to terrorism - a point I reaffirmed with my global coalition counterparts today.
"We pledged to continue to fight terrorists until their poisonous global network is totally destroyed.
"Despite Daesh's diminishing territory, it is hell-bent on directing and inspiring terrorist attacks worldwide - threatening our security at home and abroad.
"The threat they pose is evolving and intensifying, but our resolve to defeat them will not fade."
Washington wants militants captured by the coalition-backed Syrian Democratic Forces to be turned over to face justice in their home countries.
But British ministers have resisted suggestions that Alexanda Kotey and El Shafee Elsheikh should return to the UK to stand trial.
The two men were captured in Syria, having fallen into the hands of Kurdish militia fighters in January, and are under guard in the caliphate's former heartland.
US defence secretary Jim Mattis had signalled he would use the Rome meeting to press allies to take back captured militants from their countries.
But Mr Williamson has previously said he does not think the so-called Beatles "should ever set foot in this country again".
It is understood that the pair have been stripped of their British citizenship, although officials at the Home Office have refused to comment on individual cases.
Home Secretary Amber Rudd told Sky News: "The important thing is that these two people face justice.
"We will always make sure that it's properly co-ordinated and that they face justice."
Asked if the men were still British, the Home Secretary said: "I can't comment on individual cases, but we will always make sure that we keep everybody safe."
But a Whitehall source said: "The day these barbaric terrorists turned their back on this country in pursuit of an evil agenda of bloodshed and slaughter, they forfeited forever their right to return.
"They are not British subjects and should pay the price for their crimes in Syria."
Kathryn Wheelbarger, the US principal deputy assistant defence for international security affairs, said: "We're working with the coalition on foreign fighter detainees, and generally expect these detainees to return to their country of origin for disposition."