The Pentagon has begun planning for a quick pull out of American troops from Afghanistan, in case Donald Trump should repeat his sudden withdrawal of forces from Syria.

Military chiefs have begun contingency plans to evacuate forces in as little as weeks in case the US president orders a withdrawal. Sources told NBC News that the outline drawdowns were a precaution or “prudent planning” and there is currently no order to withdraw from America's longest war.

Yet the report came as American military officials admitted they had quietly cut troop numbers by 2,000 in the past year.

Mr Trump has made no secret of his disillusionment with the Afghanistan campaign and his desire to end what he sees as a costly military failure.

Mr Trump shocked commanders and allies in December 2018, by saying he would almost immediately withdraw more than 5,000 troops from the country.