Anti-Isis coalition 'preparing to launch final assault on Raqqa stronghold', US official says

Coalition spokesman says Isis has lost half of its fighters in the past 20 months

Isis fighters parade in Raqqa, which became the group's de-facto capital in Syria in August 2014. (AP)

The international coalition is preparing to launch a full-scale assault on Isis’s stronghold in Syria, a US official has claimed.

This week, the Pentagon said air strikes had killed 25,000 militants since the US and a group of regional powers started its bombing campaign more than a year and a half ago.

Speaking to the Mail on Sunday, coalition spokesman Colonel Steve Warren said Isis could have as few as 30,000 fighters left, with 600 killed in the past three weeks alone.

Air strikes against Isis-run oil and gas facilities and warehouses have slashed the organisation’s income by a third, he said.

And the international coalition is now preparing for a final assault on the city of Raqqa, Isis’s de facto capital in Syria.

Col Warren said a major bombing campaign would soon be launched against Isis targets in the city, paving the way for a ground attack by nearby Kurdish troops.

A document appeared to show fighters' salaries were being halved in Raqqa (Aleppo 24/Aymenn Jawad Al-Tamimi)

“We are not going to telegraph our timeline, because it is something they [Isis] want to know, but it is coming,” he told the Mail.

Last week, Barack Obama said in a meeting at the CIA headquarters that Isis fighters “realise their cause is lost”, with the group’s territories slashed by 40 per cent in Iraq and 10 per cent in Syria.

Isis has reportedly halved the salary it pays militants, and Col Warren said more than 100 high profile figures had been killed, mostly through drone strikes.

Colonel Steve Warren, Baghdad-based spokesman for the US-led coalition in Iraq (AP)

“Much like a boxer, Daesh [Isis] has taken several hard blows to the mid-section,” he said. “We believe the knees are getting weak, and the head is starting to drop, and they are beginning to feel the effect of the exceptional pressure we've placed on them over 20 months.”

The American military official was speaking against suggestions that the US has failed to “degrade and destroy” Isis despite carrying out tens of thousands of bombing sorties.

Isis has proven itself capable of bouncing back from recent military setbacks, and despite the threat of Russian air strikes it captured a number of villages in a major offensive against the Syrian army south of Aleppo on Friday.