Donald Trump has vowed to win the war in Afghanistan by committing more US troops as he called on Nato allies such as Britain to increase troop numbers "in line with our own".

The American President went against what he had previously said during the election campaign when he claimed the mission in Afghanistan was a waste of US efforts and vowed to pull troops out.

Yet in a surprise move President Trump claimed that a withdrawal of personnel would leave a power vacuum that to be filled by terrorists, as has happened in Iraq.

He added that the realities of life in the White House caused him to change his mind.

Mr Trump coupled his pledge with a demand for countries like Britain to do more.

In response Michael Fallon, the defence secretary, said the US commitment was "welcome" but stopped short of vowing to increase British troops beyond the additional 85 military advisers the UK has already pledged.