Prime Minister Theresa May promised on Sunday to challenge any "unacceptable" talk when she meets President Donald Trump later this week, as she tries to secure Britain's "special relationship" with the new U.S. administration. 

May, Britain's second female premier, made the comments after thousands of women marched in London on Saturday to protest about Trump's attitude to women, joining demonstrations held in major cities across the globe.

She told the BBC she would use Friday's meeting in Washington to discuss issues including future U.S.-UK trading relations, following Trump's promise to put "America first" in his inauguration speech on Friday.

Since Britons voted last year to leave the European Union, May's government has been keen to deepen ties with the United States and other nations outside Europe to show that Brexit will not diminish its standing in the world.

May indicated she would not shy away from any difficult issues, when asked about the controversy over Trump's comments on women. This erupted last year during the presidential election campaign over a 2005 video in which he boasted about grabbing women's genitals.

"I've already said that some of the comments that Donald Trump has made in relation to women are unacceptable, some of those he himself has apologised for," May said.

"When I sit down (with Trump) I think the biggest statement that will be made about the role of women is the fact that I will be there as a female prime minister," she said. "Whenever there is something that I find unacceptable I won't be afraid to say that to Donald Trump."

Trump's election has raised questions over the future of the so-called "special relationship" that has underpinned close British-American ties for decades, but the new U.S. leader has said he believes Brexit will be "a great thing".

-Reuters