Britain has agreed to send additional troops to Syria at the request of Donald Trump’s administration.

Although the number of special forces troops operating in Syria has never been made public, both the UK and France are preparing a 10-15 per cent troop increase, a US official told Foreign Policy magazine.

However, the official said “overall we have been disappointed” in efforts to persuade US allies to commit more resources to the fight against Isis.

A diplomatic source confirmed to The Independent that an increase in British troops would likely be forthcoming, without providing further details. The Ministry of Defence refused to deny the report, but added that it did not comment on the deployment of special forces as a matter of policy.

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The UK does not have an official troop presence on the ground in Syria, but a relatively low number of SAS soldiers – probably numbering in the dozens, rather than the hundreds – have been engaged in the fight against Isis in the country’s northeast. It is likely that the new commitment will amount to a small increase in special forces troops, who will remain focused on operations against Isis sleeper cells in the country.

Labour’s shadow foreign secretary, Emily Thornberry, told The Independent that increasing the UK’s deployment in Syria without consulting parliament would be evidence of “a government out of control”.

“Parliament did not agree to an open-ended commitment to military action in Syria. I have been saying for months that, now Daesh’s safe haven in Syria has been eradicated, the UK government’s strict mandate for achieving that goal is at an end, and they are duty-bound to come back to parliament and explain what their current strategy is in Syria, and seek a new mandate for that mission.”

“If they are instead going to increase the deployment of our forces to Syria without any consultation of parliament, that is just more evidence of a government out of control,” she added.

The Trump administration has been pushing its allies to replace departing US troops for some time. But confusion over the role those troops would play has delayed any further commitments.

The US had originally pitched a mostly European combat force to administer a safe zone in northern Syria, according to diplomats, which is partly designed to prevent fighting between Turkey and its bitter enemy the Kurdish-led Syrian Democratic Forces.

In response to that request, Jeremy Hunt, the foreign secretary, said that “there is no prospect of British forces replacing the Americans” in Syria. France, too, had made clear it would not remain without the US.

A parliamentary vote in 2015 authorised the UK to carry out airstrikes against Isis to “eradicate the safe haven they have established over significant parts of Iraq and Syria”. David Cameron won the vote by a majority of 174.

An increase in the UK’s special forces commitment in Syria would fill some of the gap left by the US in anti-Isis operations, but would do little to meet US plans for a safe zone.

Earlier this week, Germany turned down a request from the Trump administration to commit ground troops to Syria.

German media reports over the weekend said James Jeffrey, the US envoy for Syria, asked the government in Berlin to contribute ground troops to the anti-Isis coalition led by the US.

Steffen Seibert, a spokesperson for the government, said Germany has “made a considerable and internationally recognised contribution” to the coalition by training Iraqi troops, conducting aerial reconnaissance and refuelling allied aircraft.

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Last year, Mr Trump ordered a full withdrawal of American forces from Syria, a move which led James Mattis to resign from his position as US defence secretary.

More than 2,000 US troops were thought to be in the country at the time.

Mr Trump later partially reversed his decision, leaving around 400 troops in the country.

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Last week, the US-led coalition warned a new generation of jihadis is being created in camps holding the families of Isis fighters.

The potential for radicalisation in the camps is “the biggest long-term strategic risk” in the fight against the militant group outside of ongoing military operations, Major General Alexus Grynkewich, deputy commander of the international coalition, told The Independent.

He said: “The anecdotal stories we have about some of the women with their children who were surrendering, if you will, is that there are hardcore Isis ideologues among them. We certainly have seen reporting from some of the partners who work in those camps that there is a fair amount of that ideology.