Britain on Saturday urged China to provide "verifiable evidence" about the "safety and whereabouts" of tennis star Peng Shuai, whose whereabouts are unclear after making sexual assault allegations against a top Communist Party official.

"We are extremely concerned at the apparent disappearance of Peng Shuai, and are following the case closely," the foreign office said in a statement, adding Beijing "should urgently provide verifiable evidence of her safety and whereabouts".

"Everyone should be allowed to speak out without fear of repercussions. All reports of sexual assault, anywhere in the world, should be investigated," the statement added.

London's call for clarity follows similar demands Friday from the United States and UN, and comes as Chinese state media posted videos Saturday purporting to show Peng smiling and well.

AFP has not been able to verify the authenticity of the videos.

International pressure has been mounting this week for information about the whereabouts of the 35-year-old two-time Grand Slam doubles champion, who earlier this month accused a former vice premier of forcing her to have sex.