The state department memo, viewed by the BBC's US partner CBS News, directed US embassies on Tuesday to remove any unfilled appointments from their calendars for students seeking visas, but said those with appointments already scheduled could go ahead. The message also said the state department was preparing for an "expansion of required social media screening and vetting" applicable to all student visa applications. Trump administration seeks to pull estimated $100m in Harvard funding Foreign students who want to study in the US are usually required to schedule interviews at an American embassy in their home country before approval. When asked about student visas, state department spokesperson Tammy Bruce told reporters on Tuesday: "We take very seriously the process of vetting who it is that comes into the country, and we're going to continue to do that." The Trump administration has frozen hundreds of millions of dollars in funding for universities and moved to deport several students, while revoking thousands of visas for others. Many of these actions have been blocked by the courts. The White House has accused some US universities of failing to protect Jewish students on campus. Colleges have accused the Trump administration of trying to infringe upon free speech rights. Harvard University has been the focal point of President Donald Trump's ire. He also accuses it of flouting a Supreme Court ruling by engaging in discriminatory admissions policies. Last week, the Trump administration revoked Harvard's ability to enrol international students or host foreign researchers. A federal judge blocked the policy.