An adult film star who alleges she had an affair with US President Donald Trump in 2006, says she was threatened with violence after she first tried to go public with the story.

Stormy Daniels, whose real name is Stephanie Clifford, told CBS she was accosted by an unidentified man in 2011, who told her to "leave Trump alone".

The alleged threat came just weeks after she had agreed to sell details of her affair to a magazine.

In the US interview, she declined to discuss whether she had evidence of her affair with Trump.

Trump denies having had an affair with the actress.

Al Jazeera's Diane Eastabrook reports from Washington, DC.