New York: US President Donald Trump has bowed to public pressure by agreeing to re-lower the American flag over the White House in honour of one of his most vociferous critics, the late US senator and former Republican presidential nominee John McCain.

The White House flag was lowered to half-mast on Saturday evening after McCain's death but was returned to full-mast a day later. Trump's reversal came just hours after McCain's spokesman released a farewell statement containing clear rebukes of the President.

The official rule is that flags fly at half-mast for 24 hours after a member of Congress dies, but leaders of both political parties and military veteran groups said it was disrespectful not to keep the flags lowered for longer given McCain's legacy as a Vietnam War veteran and longtime congressman.

"It’s outrageous that the White House would mark American hero John McCain’s death with a two-sentence tweet, making no mention of his heroic and inspiring life," Joe Chenelly, executive director of veterans' group AMVETS, said.