Britain is set to deploy hundreds of elite troops to the Middle East to train Syrian rebel forces in the fight against the Islamic State (Isis), it has been reported. In a bid to break the deadlock in the war-torn nation, Royal Marines will join the SAS to provide rebel group New Syrian Army (NSA) with advanced skills.

After months of negotiating, the NSA has been persuaded to send its fighters into neighbouring Jordan for intense training, the Daily Mirror reported. After training has finished, NSA fighters will return to battle IS (Daesh) alongside SAS forces, according to the Sun.

"Tours have been extended and more are going to the region," the newspaper quoted an unidentified senior source as saying. "The government is throwing absolutely everything at this, money and manpower, everything is being hurled at the problem."

Earlier this week photographs of British special forces operating on the ground in Syria emerged. The troops were pictured driving the Al-Thalab, a high-mobility long-range patrol vehicle designed for surveillance, reconnaissance, internal security and border patrol forces.

The NSA is a moderate rebel force and mainly consists of Syrian Arab army defectors. The group was established in 2015 with US backing to fight against IS in Deir ez-Zor province, which is largely controlled by the terrorist organisation.

MI6 and France's foreign spy service, the DGSE, are also training agents recruited from refugee camps in Jordan. Once they are inside Syria, the agents provide intelligence information on the civil war.

Preventing IS fighters from permeating NSA ranks has been a key issue. "The aim is to raise the level of training and capability for these forces," an unidentified source said.

"As we understand the vetting process has now been agreed, it has been a challenge, as many of these guys are 'clean skins' they have little background data that can be checked other than their word.

"But the Americans have established a simple but robust process that we will need to monitor and observe throughout the trainees' time in the camps. The biggest threat is of infiltration by Isis".

Statistics from the US-led bombing campaign in Iraq and Syria showed that more than 14,000 air strikes were conducted at a cost of £6.4bn ($8.4bn) to the US and £280m ($365m) to the UK. Around 3,800 US soldiers are in Iraq and US, UK and French special forces are present there and in neighbouring Syria, Sky News reported.