British military personnel have arrived in the Middle East to train "moderate" Syrian opposition forces as they attempt to open up a second front around Islamic State (IS) stronghold Raqqa.
Defence Secretary Sir Michael Fallon said the Syrian forces were being trained in infantry, medical and explosive hazard awareness skills.
He spoke ahead of a London summit with defence ministers from the coalition of countries fighting IS, also known as Daesh, in Iraq and Syria.
It comes after a ceasefire between Syrian rebels and the Russian-backed Bashar Assad regime in Aleppo broke down, threatening plans to evacuate civilians amid reports of pro-government troops executing non-combatants.
At the meeting, Sir Michael will reveal that he has agreed to "surge" the number of data recovery experts to exploit material obtained as IS forces are defeated or flee from Mosul in Iraq.
Britain's top commander in the region, Major General Rupert Jones, said recently that plans revealing thousands of IS plots to attack Europe were discovered after the terrorists were driven out of Manbij, northern Syria.
Sir Michael hopes the extra experts will be able to exploit data and technical equipment seized from IS to help track UK militants, win the battle on the ground, better understand the militants' structure and leadership, and build a case against fighters who have committed atrocities.
The summit will also mark US Defence Secretary Ash Carter's last official visit to the UK before he is replaced by Donald Trump's appointee General James "Mad Dog" Mattis.
Ahead of the summit, Sir Michael said: "Daesh is being taken on in eastern Mosul: last week we opened up a second front around Raqqa. Daesh is losing ground, finance, and fighters.
"As part of the 68-member coalition, Britain is playing a leading role, through our air strikes, intelligence, surveillance and reconnaissance, and our training.
"In 2017 we must maintain momentum to deal these terrorists a decisive blow."
In recent days RAF jets have bombed IS buildings, positions and equipment around Mosul, while the coalition has carried out more than 300 air strikes in support of the Syrian Democratic Forces' operation in Raqqa, where the UK has hit weapons factories, IS strongholds and anti-aircraft guns.
The RAF is working more intensely on a single operation than at any point in 25 years, the Ministry of Defence said.
Warplanes flew almost 14,000 hours over the last year, compared to 5,600 during the most intense 12 months in Afghanistan.
Since June, over 70% of UK air strikes have been in support of the Iraqi advance in Mosul.
In addition, 80 engineers from 22 Engineer Regiment are to extend their tour of duty by six months in order to carry out upgrades to the Al Asad air base in Iraq, where UK soldiers are training Iraqi forces.
It comes after the chief of the defence staff warned that IS terrorists were "moving in migrant flows" and "hiding in plain sight" all over the world, in tactics that should make Britain think about how it "manages identity".
In comments that could reignite the debate around identity cards, Sir Stuart Peach said he was "worried" about the global reach of IS militants, who deliberately destroy their identity documents to travel illegally into other countries where they could carry out attacks.
The most senior officer in the armed forces said IS, also known as Daesh, represented the closest danger and a "call to action" going beyond UK and coalition air strikes in Syria and Iraq.
In his first annual lecture to the Royal United Services Institute (RUSI) on Wednesday, Sir Stuart said: "I worry about the global reach of Daesh as an idea - copycat, using the internet - more than the internet - using social media, popping up all over the world.
"The Chinese state has accepted they have a problem.
"This is not now a localised phenomenon, it is now a wider phenomenon.
"And of course we face, as my friend Andrew Parker has said, the director general of MI5, a potential network of combat-experienced terrorists.
"On the other hand they are losing territory rapidly, foreign fighters are being killed and displaced.
"But they are moving in migrant flows, hiding in plain sight.
"One of the obvious deductions, and I think it does bear more scrutiny from the younger and the analytical community, is how we manage identity in a world where people are deliberately trying to destroy their identity documents and/or they move in migrant flows."