US President Donald Trump's administration has ordered its missions abroad to stop scheduling new appointments for student and exchange visitor visa applicants as the State Department prepares to expand social media vetting of foreign students, according to an internal cable seen by the Reuters news agency on Tuesday.

US Secretary of State Marco Rubio said in the cable that the department plans to issue updated guidance on social media vetting of student and exchange visitor applicants after a review is completed and advised consular sections to halt the scheduling of such visa appointments.

The move comes as the Trump administration has sought to ramp up deportations and revoke student visas as part of its wide-ranging efforts to fulfil his hardline immigration agenda.

In the cable, first reported by Politico, Rubio said appointments that have already been scheduled can proceed under the current guidelines, but available appointments not already taken should be pulled down.

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

"The Department is conducting a review of existing operations and processes for screening and vetting of student and exchange visitor (F, M, J) visa applicants, and based on that review, plans to issue guidance on expanded social media vetting for all such applicants," the cable said.

The expanded social media vetting will require consular sections to modify their operations, processes and allocation of resources, according to the cable, which advises the sections going forward to take into consideration the workload and resource requirements of each case before scheduling them.

The cable also advises consular sections to remain focused on services for US citizens, immigrant visas and fraud prevention.

Trump administration officials have said student visa and green card 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 US foreign policy and accusing them of being pro-Hamas.

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

A Tufts University student from Turkey was held for over six weeks in an immigration detention centre in Louisiana after co-writing an opinion piece criticising her school's response to Israel's war in Gaza.

She was released from custody after a federal judge granted her bail.

Last week, the Trump administration moved to revoke Harvard's ability to enroll international students. Those roughly 6,800 students make up about 27 percent of Harvard's total enrollment.

The Republican president's administration has moved to undermine the financial stability and global standing of the nation's oldest and wealthiest university after it pushed back on government demands for vast changes to its policies. (Reuters)