Soldiers from the SDF (Picture: PA).
Kurdish-led forces are fighting a "very fierce" battle against the so-called Islamic State in their last stronghold in eastern Syria.
A spokesman for US-backed and Kurdish-led Syrian Democratic Forces (SDF) told the Associated Press (AP) news agency that the "the most experienced" jihadists are defending their last territory.
On Saturday, the SDF announced they had launched an offensive on the eastern province of Deir el-Zour in a final push against IS, also known as 'Daesh'.
This came after more than 20,000 civilians were evacuated from the IS-held area.
SDF spokesman Mustafa Bali told AP: "The battle is very fierce. Those remaining inside are the most experienced who are defending their last stronghold. According to this you can imagine the ferocity and size of the fighting."
Since 2014, RAF aircrew based in Cyprus have been flying near daily missions over Iraq and Syria as part of a coalition of nations fighting IS.
Operation Shader began as a humanitarian aid mission but has grown into a complicated mission to try and defeat IS.
The UK has been the second biggest contributor to the coalition of nations fighting IS, only behind the United States.
US President Donald Trump predicted that IS will have lost all the territory it once controlled in Iraq and Syria by next week.
President Trump previously said IS were "doomed" as he announced the withdrawal of all 2,000 US troops from the country.
That announcement reportedly led to the resignation of then-Defense Secretary General James Mattis, who wrote in his resignation letter: "You have a right to have a secretary of defense whose views are better aligned with yours."
The Kurdish-led SDF launched its offensive to end the IS presence in Syria in September, a battle that left hundreds of fighters dead on both sides.