BRITAIN is thought unlikely to increase troop numbers in Afghanistan in the wake of Donald Trump's announcement that he is to scale up the US military presence in the country.

In a dramatic turnaround from his election campaign calls for the 16-year war to be brought to an end, the US President unveiled a new south Asia strategy designed to prevent a Taliban takeover of Afghanistan, target Islamic State and al Qaeda and stop mass terror attacks in America. He said he was "confident" that Nato allies - which include Britain - would hike troops and funding in line with the US.

Sir Michael Fallon, the Defence Secretary, welcomed the President's move, saying the allies must "stay the course" in Afghanistan.

But in a statement responding to the announcement, the Scot gave no indication that the UK was considering an increase to its 500-strong deployment and stressed that an additional 85 troops were committed as recently as June.

Sir Michael was briefed by his US counterpart, Jim Mattis, ahead of Mr Trump’s announcement, in the first of a series of phone calls to Nato allies.

But it is understood that London has received no formal request from the US for further military support and UK sources played down the prospects of an increase in British boots on the ground.

Sir Michael said: "The US commitment is very welcome. In my call with Secretary Mattis yesterday we agreed that, despite the challenges, we have to stay the course in Afghanistan to help build up its fragile democracy and reduce the terrorist threat to the West.

"It's in all our interests that Afghanistan becomes more prosperous and safer: that's why we announced our own troop increase back in June."

But Jo Swinson, the Liberal Democrat deputy leader, noted how the Government's rapid praise for Mr Trump contrasted with its failure to condemn his “divisive views” in the past.

"For once, sense seems to have prevailed in the White House,” declared the Scottish MP.

"But to succeed in Afghanistan will require winning the hearts and minds of its people and working closely with neighbouring countries. On that front, Donald Trump has already done untold damage through his proposed refugee ban, Islamophobic comments and cack-handed approach to foreign affairs.”

She added: "Simply pouring more troops into Afghanistan will not work without a broader strategy involving careful diplomacy and redoubled efforts to build a stable government."

Mr Trump made repeated calls ahead of his election for US troops to be withdrawn from Afghanistan, where they have been involved in military operations since the 2001 war to topple the Taliban following the 9/11 attacks.

But in an address to the nation from Fort Myer, near Washington DC, on Monday night, the President acknowledged that he had changed his mind on the issue and decided to go against his "original instinct".

In a speech evoking the 9/11 events in 2001 which drew the US into the war, as well as the recent terror attack in Barcelona, Mr Trump said American policy would now focus not on nation-building but on killing terrorists.

His comments came after Pentagon officials proposed a 4,000-troop increase to the 8,400-strong US deployment in the country, to bolster the Kabul government, train Afghan forces and fight the Taliban and other militant groups.

"From now on, victory will have a clear definition: attacking our enemies, obliterating Isis, crushing al Qaeda, preventing the Taliban from taking over Afghanistan and stopping mass terror attacks against America before they emerge," said Mr Trump.

"We will ask our Nato allies and global partners to support our new strategy with additional troop and funding increases in line with our own - we are confident they will."

Before his election, Mr Trump made repeated calls for the US to withdraw, saying lives and money were being "wasted".

But Monday's announcement came after discussions with top Pentagon advisers and the intelligence community as well as Vice President Mike Pence and Mr Mattis.

Mr Trump said his reversal in opinion had come after studying Afghanistan from "every conceivable angle".

"My original instinct was to pull out and historically I like following my instincts, but all my life I've heard that decisions are much different when you sit behind the desk in the Oval Office," he said.

He said he would not put a timescale on the end of the war but would instead wait for certain conditions to be met on the ground.

And he declined to discuss further details on troop numbers, saying: "America's enemies must never know our plans."

Mr Trump's announcement was welcomed by Jens Stoltenberg, the Nato Secretary-General, who noted that recent weeks had seen more than 15 member states pledging additional contributions to its mission in the country, where the alliance currently has more than 12,000 troops deployed.

"I welcome President Trump's new, conditions-based approach to Afghanistan and the region," said Mr Stoltenberg. "Nato remains fully committed to Afghanistan and I am looking forward to discussing the way ahead with Secretary Mattis and our allies and international partners."

Then-president George W Bush sent troops into Afghanistan after the 9/11 attacks and his successor, Barack Obama, increased the military presence to more than 100,000 but failed to bring the war to a close as planned.

Britain provided the second largest contribution to Nato operations in Afghanistan following 9/11, with around 9,500 UK troops deployed in Helmand province alone at its peak. British combat troops left Afghanistan in 2014, with a small contingent remaining on the ground to train local military forces.

A total of 456 British forces personnel and Ministry of Defence officials have died while serving in the country since the start of operations in October 2001.