President Donald Trump has cancelled a "secret" summit with Taliban leaders and his Afghan counterpart after the insurgent group claimed responsibility for a deadly attack in Kabul that killed an American soldier and 11 others, dealing a body blow to protracted negotiations that were nearing a peace deal to end America's longest war.

In a series of tweets on Saturday, Trump disclosed that he was to meet Afghan President Ashraf Ghani and senior Taliban leaders on Sunday at his Camp David retreat. But he cancelled the meeting after the Taliban admitted it was behind a suicide car bomb attack on Thursday that had killed an American soldier and 11 others in the capital of Kabul.