Washington (AFP)

President Donald Trump said on Friday that China's behavior towards Hong Kong was "a tragedy" for the world and announced restrictions on Chinese students from entering the United States.

Beijing "has not kept its word given to the world to ensure the autonomy of Hong Kong," he said in a brief statement from the White House gardens.

"It is a tragedy for the people of Hong Kong, for China, and for the whole world," he added.

The United States has been denouncing for several days the controversial national security law that Beijing wants to impose on Hong Kong. They believe it is a disguised way of muzzling the Hong Kong opposition and cutting corners, which China firmly denies.

Expressing his desire to better secure "the university research vital to the country", Mr. Trump announced the suspension of the entry of "certain nationals of China who we have identified as potential security risks".

The American president, however, remained elusive about the exact scope of this decision and the number of students who could be affected.

The White House tenant also announced that he is launching the process of eliminating the exemptions granted to Hong Kong as part of the revocation of his special status.

"This decision will have an impact on all the agreements we have with Hong Kong," he added, referring in particular to the extradition treaty.

The handover of Hong Kong was done in the name of the principle "One country, two systems" which allowed the territory to preserve unknown liberties in mainland China, in particular a free economy, independent justice, freedom of expression and a Parliament partially elected by universal suffrage.

These derogations have led many countries, such as the United States, to pass laws authorizing them to treat Hong Kong as a commercial entity separate from the authoritarian Chinese regime.

© 2020 AFP