This video can not be played
The US says it is "deeply concerned" about Chinese tennis star Peng Shuai, who has not been heard from since making sexual assault allegations against a top Communist Party official.
The White House urged China to "provide independent, verifiable proof" of Ms Peng's whereabouts and safety.
The 35-year-old doubles Grand Slam winner accused China's ex-vice-premier of sexual assault two weeks ago.
The Women's Tennis Association has threatened to pull events out of China.
WTA chairman Steve Simon told the BBC there will be no competitions in China next year without proof that Ms Peng was safe.
"We cannot stand by compromises. This is a right and wrong issue," he said.
The WTA has been told Ms Peng is safe, and in Beijing, by the Chinese Tennis Association, although Mr Simon said there has been no confirmation that is true.
- Naomi Osaka voices concern over Peng Shuai
- Tennis star accuses top Chinese official of abuse
- Peng 'must be heard' on sex abuse claim
In a separate development on Friday, three photos of Ms Peng were posted on a WeChat account under her name with the caption "Happy Weekend".
However, the authenticity of the post on the Chinese instant messaging service was questioned by BBC China media analyst Kerry Allen.
From an account called “Peng Shuai 2” with a Chinese flag avatar? 🧐 https://t.co/LBGCX3blH6
— Kerry Allen 凯丽 (@kerrya11en) November 19, 2021
The BBC is not responsible for the content of external sites.View original tweet on Twitter
Earlier this week, Chinese state media released an email attributed to Ms Peng, but Mr Simon cast doubt about its authenticity.
The former number one-ranked doubles player has not been seen in public since posting an allegation about former Vice-Premier Zhang Gaoli on Chinese social media site Weibo on 2 November.
She alleged she was "forced" into sexual relations with Mr Zhang – who served as the country's vice-premier between 2013 and 2018.
The post was taken down minutes later, along with other recent posts from the account, which has more than 500,000 followers.
Leading voices from the world of tennis have increasingly spoken out about Ms Peng since.
This video can not be played
Former women's world number one and 23-time Grand Slam winner Serena Williams said news of Ms Peng's disappearance had left her "devastated and shocked".
"I hope she is safe and found as soon as possible. This must be investigated and we must not stay silent," she added in a tweet.
World number one male tennis player Novak Djokovic said he was shocked, while Naomi Osaka also voiced concerns about her whereabouts.
More tennis players and social media users have since posted under the hashtag #WhereIsPengShuai.
Ms Peng is a prominent figure in Chinese tennis. She has won two women's doubles Grand Slams at Wimbledon in 2013 and the 2014 French Open, both alongside Taiwan's Hsieh Su-wei.
Her allegation is the highest profile incident in China's fledgling #MeToo movement.