All 55 million foreigners who hold US visas are subject to continuous review, the State Department warned on Thursday, as President Donald Trump tightens measures against visas and immigration.

"The State Department's ongoing reviews include all 55 million foreign nationals who currently hold valid US visas," a State Department official said. "The State Department revokes visas whenever there are indications of potential ineligibility, which includes overstaying, criminal activity, threats to public safety, involvement in any form of terrorist activity, or providing support to a terrorist organization."

The official did not say that all 55 million visas were under active review, but clearly stated that the Trump administration considers the review to be "fair game." The official, speaking on condition of anonymity, said the Trump administration was tightening controls, particularly on students. "We are reviewing all student visas," the official said, stating that the State Department was "constantly monitoring what people have been saying" on social media.

Secretary of State Marco Rubio is targeting anti-Israel protesters using a vague law that allows him to revoke visas for people deemed to be contrary to US foreign policy interests.

The State Department said earlier that it had revoked 6,000 visas since Rubio took office in January with Trump. That is four times more student visas than President Joe Biden's administration revoked during the same period last year, according to the State Department. Rubio argues that the administration has the right to issue and revoke visas without judicial review and that non-US citizens do not enjoy the US constitutional right to freedom of speech.

But the administration has faced setbacks in two of the most high-profile cases. Mahmoud Khalil, a lawful permanent resident of the United States who led pro-Palestinian protests at Columbia University, was released in June by a judge. Rumeysa Ozturk, a Turkish doctoral student at Tufts University who wrote an article in a university newspaper criticizing Israel, was released by a judge in May pending court hearings. | BGNES, AFP