Isis has lost a staggering number of jihadists and has only killed three US troops in return, making the US-to-Isis "kill ratio" 15,000-to-one.

Earlier this year, President Barack Obama declared the group had lost swathes of territory and said its fighters "realise their cause is lost".

The US president said the so-called Islamic State had lost 40 per cent of its "caliphate" in Iraq and 10 per cent in Syria, and had suffered numerous financial setbacks.

In pictures: Civilians freed from Isis in Manbij Show all 11 1 /11 In pictures: Civilians freed from Isis in Manbij In pictures: Civilians freed from Isis in Manbij Women and children celebrating after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A man cuts the beard of a civilian who was freed from Isis by the SDF in Manbij on 12 August Reuters In pictures: Civilians freed from Isis in Manbij Women carry newborn babies while running after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman freed from Isis hugs an SDF fighter in Manbij on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman adding her veil to a pile of niqabs burning in Manbij, Syria, after being freed from Isis on 12 August Reuters In pictures: Civilians freed from Isis in Manbij Children celebrating on top of a lorry after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A man and child freed from Isis by the SDF in Manbij on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman carrying her children walks towards SDF fighters after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman and child freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij An SDF fighter kisses a crying man who was freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij Hundreds of civilians freed from Isis in Manbij, Syria, on 12 August Reuters

The number of Isis militants killed in US strikes has increased from 6,000 in January 2015 to 45,000 in July 2016, Time reports.

Isis has recently lost control of its last territories on the border with Turkey, isolating it from the rest of the world and strangling its ability to bring in new recruits.

The area previously controlled by Isis has been taken by the rebel Free Syrian Army, backed by a Turkish ground offensive that began at the town of Jarablus on 24 August.

On Saturday, more Turkish tanks rolled over the border into Al-Rai, a town some 55km (34 miles) west of Jarablus, and over the weekend a pincer Turkish-rebel offensive has closed the gap between the two.

Advances by Iraq's army and allied militia towards its most important possession of Mosul have put the group under renewed pressure.

Baghdad could retake Mosul by the end of the year, Joseph Votel, the head of the US military's Central Command said on Tuesday.

Turkish-backed rebels have been closing in on Isis on two sides from Jarablus (circled in NE) and Al-Rai (circled to W), leaving only a tiny stretch still connecting Isis with the rest of the world. It became apparent Isis was losing control of the border area when the key town of Manbij (circled, SE) fell in early August

One of the terror group's most senior figureheads was killed in Syria last month.

Abu Muhammed al-Adnani was “martyred while surveying the operations to repel the military campaigns against Aleppo [province],” the group's Amaq news agency said, without providing further details.

Syrian women burn burkas to celebrate liberation from Isis

A US defence official told Reuters the United States targeted Adnani in a strike on a vehicle travelling in the Syrian town of al-Bab. The official stopped short of confirming Adnani's death, however.

Adnani was believed to be the second most important leader of Isis after Abu Bakr al-Baghdadi and was one of the group's longest-serving members.

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The group said his death would not harm it and said his killers would face "torment" in a statement in their al-Naba newspaper, according to the Site Intelligence monitoring group.

"Today, they rejoice for the killing ... and then they will cry much when Allah will overpower them, with His permission, with affliction of the worst torment by the soldiers of Abu Muhammad and his brothers," the statement said.

Among senior Isis officials killed in air strikes this year are Abu Ali al-Anbari, Baghdadi's formal deputy, and the group's "minister of war", Abu Omar al-Shishani.