By Humeyra Pamuk

WASHINGTON (Reuters) -The Trump administration on Thursday ordered a social media vetting for all U.S. visa applicants who have been to the Gaza Strip on or after January 1, 2007, an internal State Department cable seen by Reuters showed, in the latest push to tighten screening of foreign travelers.

The order to conduct a social media vetting for all immigrant and non-immigrant visas should include non-governmental organization workers as well as individuals who have been in the Palestinian enclave for any length of time in an official or diplomatic capacity, the cable said.

"If the review of social media results uncovers potential derogatory information relating to security issues, then a SAO must be submitted," the cable said, referring to a security advisory opinion, which is an interagency investigation to determine if a visa applicant poses a national security risk to the United States.

The cable was sent to all U.S. diplomatic and consular posts.

The move comes as President Donald Trump's administration has revoked hundreds of visas across the country, including the status of some lawful permanent residents under a 1952 law allowing the deportation of any immigrant whose presence in the country the secretary of state deems harmful to U.S. foreign policy.

The cable dated April 17 was signed by U.S. Secretary of State Marco Rubio, who said in late March that he may have revoked more than 300 visas already.

The State Department did not immediately respond to a request for comment.

Trump officials have said student visa holders are subject to deportation over their support for Palestinians and criticism of Israel's conduct in the war in Gaza, calling their actions a threat to U.S. foreign policy interests.

Trump's critics have called the effort an attack on free speech rights under the First Amendment of the U.S. Constitution.

The U.S. Constitution guarantees freedom of speech for everyone in the U.S., regardless of immigration status. But there have been high-profile instances of the administration revoking visas of students who advocated against Israel's war in Gaza.

Among the most widely publicized of such arrests was one captured on video last month of masked agents taking a Tufts University student from Turkey, Rumeysa Ozturk, into custody.

When asked about Ozturk at a news conference last month, Rubio said: "Every time I find one of these lunatics, I take away their visas" and he warned there would be more individuals whose visas could be revoked.

(Reporting by Humeyra Pamuk; Editing by Jamie Freed)