The White House says it is monitoring the massing of Chinese troops on Hong Kong's border.
The protests against China and Hong Kong's Chief Executive Carrie Lam have not stopped, and there are fears that Beijing is about to use military force to stamp out the student-led protest movement.
An unnamed White House official says units of the Chinese military or armed police have gathered at the border with Hong Kong. But the official stressed that the nature of the buildup was not clear. Some have suggested it could simply be a large scale swearing in of police recruits.
But Hong Kong police are being worn down in almost daily combat with protestors. And a Chinese foreign ministry spokesperson, Hua Chunying, said, "If the White House really cares about a peaceful, stable and prosperous Hong Kong, it should admonish the violent and radical protesters to express their demands through peaceful means instead of violence."
She also said she was not aware of a situation on the China-Hong Kong border.
But China has long said the protests in Hong Kong are a "creation of the US."