WASHINGTON — The Trump administration asked federal agencies Tuesday to cancel contracts with Harvard University worth about $100 million, intensifying the president’s clash with the nation’s oldest and wealthiest university.

The government already has canceled more than $2.6 billion in federal research grants for the Ivy League school, which has pushed back on the administration’s demands for changes to several of its policies.

A letter sent Tuesday from the General Services Administration, which oversees contracting and real estate for the federal government, directed agencies to review contracts with the university and seek alternate arrangements.

The New York Times first reported on the letter.

In another development on the education front, Secretary of State Marco Rubio ordered U.S. embassies worldwide to stop scheduling interviews for student visas as the Trump administration weighs stricter vetting of applicants’ social-media profiles.

The directive, laid out in a cable sent to diplomats worldwide on Tuesday, marks the latest effort by the administration to restrict foreign students’ entry to American schools over claims that they might threaten U.S. national security or promote antisemitism.

“Effective immediately, in preparation for an expansion of required social media screening and vetting, consular sections should not add any additional student or exchange visitor (F, M and J) visa appointment capacity until further guidance is issued,” Rubio wrote. He said that guidance is expected in the coming days.

The cable says interviews that have already been scheduled can go ahead.

President Donald Trump has railed against Harvard, calling it a hotbed of liberalism and antisemitism. The school filed a lawsuit April 21 over the administration’s calls for changes to the university’s leadership, governance and admissions policies. Since then, the administration has slashed the school’s federal funding, moved to cut off enrollment of international students and threatened its tax-exempt status.

The administration has identified about 30 contracts across nine agencies to be reviewed for cancellation, according to an administration official who was not authorized to speak publicly and provided details on the condition of anonymity.

The contracts total roughly $100 million, according to a senior administration official, who spoke on the condition of anonymity to describe internal deliberations. The contracts include executive training for Department of Homeland Security officials, research on health outcomes related to energy drinks and a contract for graduate student research services.

Agencies with contracts that are deemed critical are being directed not to halt them immediately, but to devise a plan to transition to a different vendor other than Harvard.

The letter applies only to federal contracts with Harvard and not its remaining research grants.

Trump laid into Harvard on social media over the weekend, threatening to cut an additional $3 billion in federal grants and give it to trade schools across the United States. He did not explain which grants he was referring to or how they could be reallocated.

The president also accused Harvard of refusing to release the names of its foreign students. In a new line of attack, he argued that students’ home countries pay nothing toward their education and that some of the countries are “not at all friendly to the United States.”

International students are not eligible for federal financial aid, but Harvard offers its own aid to foreign and domestic students alike.

“We are still waiting for the Foreign Student Lists from Harvard so that we can determine, after a ridiculous expenditure of BILLIONS OF DOLLARS, how many radicalized lunatics, troublemakers all, should not be let back into our Country,” Trump said on social media.

It was not clear exactly what the president was referring to. The federal government already has access to visa information and other records on foreign students at Harvard and other universities.