(Reuters) -The U.S. State Department's continuous vetting applies to "all of the more than 55 million foreigners who currently hold valid U.S. visas," a department official said on Thursday, including those who have already been admitted to enter the country.

"The State Department revokes visas any time there are indications of a potential ineligibility, which includes things like any indicators of overstays, criminal activity, threats to public safety, engaging in any form of terrorist activity, or providing support to a terrorist organization," the official said.