Donald Trump marked his third 9/11 anniversary as president with a moment of silence as his frustration grows over what he calls the “endless war” in Afghanistan, where al Qaida conceived the attacks.

It has been 18 years since al Qaida hijackers commandeered four US commercial airliners and crashed them into the World Trade Centre, the Pentagon and a field in Shanksville, Pennsylvania.

Like Presidents Barack Obama and George W. Bush, Mr Trump is marking the day with the war still raging.

Mr Trump participated in a moment of silence on Wednesday on the White House South Lawn with first lady Melania Trump and White House staff.

He was going to the Pentagon afterwards to honour the nearly 3,000 people who died in the largest attack on American soil.