Washington DC - The State Department's number two on Thursday threatened to strip visas over online support for the killing of right-wing political influencer Charlie Kirk, encouraging internet users to flag foreigners' posts.

"In light of yesterday's horrific assassination of a leading political figure, I want to underscore that foreigners who glorify violence and hatred are not welcome visitors to our country," Deputy Secretary of State Christopher Landau wrote on X.

"I have been disgusted to see some on social media praising, rationalizing, or making light of the event, and have directed our consular officials to undertake appropriate action," he wrote, without naming specific posts.

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Landau quickly received replies that pointed to specific online comments and which encouraged him to revoke visas purported to belong to foreign residents in the US.

Landau responded in turn, asking X users to keep sharing by replying to him online. He promised to ask the State Department to look into the posts.

Kirk, a 31-year-old ally of President Donald Trump who has helped galvanize conservative support among young people, was shot dead during a speaking engagement Wednesday at a university in Utah.

The Trump administration has moved aggressively to revoke or deny visas as part of a broader crackdown on immigration.

As of mid-August, the State Department said it has rescinded 6,000 student visas, mostly over legal violations including overstays or police encounters like drunk driving.

Secretary of State Marco Rubio has also said he is prioritizing the revocation of visas of "lunatics" who led campus protests against Israel's genocidal offensive in Gaza, using a law that allows him to remove people for going against US foreign policy interests.

Under Rubio's orders, the State Department now asks all visa applicants to keep their social media profiles open for vetting.

The approach comes despite outspoken criticism by the Trump administration over restrictions on online speech in European allies, including over alleged incitement by far-right groups.