The Trump administration said Thursday that it is reviewing more than 55 million people who have valid U.S. visas for any violations that could lead to deportation, marking a growing crackdown on foreigners who are even permitted to be in the United States.

In a written answer to a question from The Associated Press, the State Department said all U.S. visa holders, which can include tourists from many countries, are subject to “continuous vetting,” with an eye toward any indication that they could be ineligible for permission to enter or stay in the United States.

Should such information be found, the visa will be revoked, and if the visa holder is in the United States, he or she would be subject to deportation.

Since President Donald Trump took office, his administration has focused on deporting migrants illegally in the United States as well as holders of student and visitor exchange visas.

The State Department’s new language suggests that the continual vetting process, which officials acknowledge is time-consuming, is far more widespread and could mean even those approved to be in the U.S. could abruptly see those permissions revoked.

The department said it was looking for indicators of ineligibility, including people staying past the authorised timeframe outlined in a visa, criminal activity, threats to public safety, engaging in any form of terrorist activity or providing support to a terrorist organisation.

“We review all available information as part of our vetting, including law enforcement or immigration records or any other information that comes to light after visa issuance, indicating a potential ineligibility,” the department said.

The administration has steadily imposed more restrictions and requirements on visa applicants, including requiring them to submit to in-person interviews.

The review of all visa holders appears to be a significant expansion of what had initially been a process focused mainly on students who have been involved in what the government perceives as pro-Palestinian or anti-Israel activity.

Officials say the reviews will include all visa holders’ social media accounts, law enforcement and immigration records in their home countries, along with any actionable violations of U.S. law committed while they were in the United States.

“As part of the Trump Administration’s commitment to protect U.S. national security and public safety, since Inauguration Day, the State Department has revoked more than twice as many visas, including nearly four times as many student visas, as during the same time period last year,” the State Department said.

The vast majority of foreigners seeking to come to the U.S. require visas, especially those who want to study or work for extended periods. Among the exceptions for short-term tourist or business visits are citizens of the 40 mainly European and Asian countries belonging to the Visa Waiver Program, which grants those nationals a stay of up to three months without having to apply for a visa.

But large swaths of the world — including highly populated countries like China, India, Indonesia, Russia and most of Africa — are not part of the program, meaning their citizens must apply for and receive visas to travel to the United States.

Earlier this week, the department said that since Trump returned to the White House, it has revoked more than 6,000 student visas for overstays and violations of local, state and federal law, the vast majority of which were assault, driving under the influence of alcohol or drugs and support for terrorism.

It said about 4,000 of those 6,000 were due to actual infractions of laws and that approximately 200 to 300 visas were revoked for terrorism-related issues, including providing support for designated terrorist organisations or state sponsors of terrorism.