Scarlett Johansson has lashed out at Ivanka Trump by calling her "cowardly" and "uninspired" for failing to publicly speak out against US President Donald Trump's policies.

"It was really baffling. You can't have it both ways," The Ghost in the Shell star said at the Women in the World Summit on Thursday (6 April). "If you take a job as a public advocate, then you have to advocate publicly."

The Captain America: Civil War star also was not pleased with Ivanka, the special assistant to the US president, for saying she stands up to her father behind closed doors.

"I thought to myself, 'Well, that's empowering,'" she jokingly said, as quoted by Us Weekly.

"How old-fashioned, this idea that behind a great man is a great woman. What about being in front of that person or next to that person? ... Powerful women often get concerned with this idea that they're going to be seen in this unforgiving light. Screw that. ... It's so uninspired and actually really cowardly. And I was so disappointed by that interview she gave yesterday."

Johansson slammed the first daughter after the latter said earlier this week that she was fine with people calling her "complicit", but she is a "force for good".

Oscars 2017
Scarlett Johansson and Ivanka Trump

"So I hope to make a positive impact. I don't know what it means to be complicit, but, you know, I hope time will prove that I've done a good job," Ivanka had said.

Ivanka, 35, made the comments after the 32-year-old actress had impersonated the former fashion designer on Saturday Night Live. In the act, Johansson appeared as Ivanka for an advertisement for a perfume called "Complicit." "The fragrance for the woman who can stop all this ... but won't," Johansson had said.