In the lawsuit, filed by Los Angeles attorney Michael Avenatti, Daniels argues that because the agreement is invalid, she's under no obligation to remain silent. But the lawsuit says attempts to "intimidate" her "into silence and 'shut her up' in order to 'protect Mr Trump' continue unabated".

As recently as February 27 of this year, Cohen began "a bogus arbitration proceeding" against Daniels in Los Angeles to keep her quiet, the lawsuit argues. The agreement, attached as an exhibit to the lawsuit, specifies arbitration as a way to resolve disputes.

Last month, Cohen admitted to paying Daniels $US130,000 ($167,000) but did not say what the payment was for. He said he used his personal funds to "facilitate" the payment and was not reimbursed by the Trump campaign or the Trump Organisation.

The Wall Street Journal reported in January that Cohen arranged the payment with Daniels to keep her from publicly discussing the alleged sexual encounter during the presidential campaign.

After the report, In Touch published a 2011 interview with Daniels in which she claimed she and Trump had a sexual encounter after meeting at a golf tournament in Lake Tahoe, Nevada, a year after his marriage to Melania Trump.

In the lawsuit, Daniels argues that Trump likely knows about Cohen's ongoing attempts to silence her because the rules of the New York Bar Association, of which Cohen is a member, require that he keep his client informed of his activities.

"It strains credulity to conclude that Mr Cohen is acting of his own accord without the express approval and knowledge of his client Mr Trump," the lawsuit adds

The lawsuit against the US President from the former porn star comes amid days of upheaval in, and staff departures from, the Trump White House.

Last week, communications director Hope Hicks, a trusted aide, announced her departure. On Tuesday, White House economic adviser Gary Cohn announced his resignation after a fierce debate with Trump over the President's plan to impose tariffs on foreign-made steel and aluminium.

USA Today