Washington: President Donald Trump's contention that women who accused him of sexual harassment were lying was just a political opinion expressed during the 2016 campaign, his lawyers argued as they sought to block a suit by a woman who appeared on his reality TV show, "The Apprentice."

Summer Zervos sued Trump in January, saying he defamed her by denying that he had groped her and calling women who accused him of similar behaviour liars. Trump lashed out while on the campaign trail in October against what he called "phony" accusations, saying he was being attacked with lies and slander.

In a filing late Tuesday, Trump's lawyer called her lawsuit politically motivated. Zervos can't hold Trump liable for engaging in "political speech in the context of a public debate," which is protected by the First Amendment, Marc Kasowitz wrote.

"Mr. Trump was merely defending his character and qualifications for office from the false attacks Ms Zervos levelled against him just a few weeks before the presidential election," Kasowitz wrote in the filing.