President Donald Trump signed a proclamation to suspend international visas for new students at Harvard University, the White House announced Wednesday, in a dramatic escalation of its efforts to block foreigners from enrolling at the elite university.

The university called it “yet another illegal retaliatory step” from an administration that has sought ways to circumnavigate the courts in its push to bar foreign students.

Donald Trump has suspended for an initial six months the entry of foreign students seeking to study or participate in exchange programmes at Harvard University.