A federal judge has blocked another effort by the Trump administration to keep international students from attending Harvard University, saying officials' “misplaced efforts to control a reputable academic institution” threatened freedom of speech.

The order on Monday from district judge Allison Burroughs in Boston preserves the ability of foreign students to travel to the United States for studies at Harvard while the case is decided.

President Donald Trump has sought to cut off Harvard’s enrollment of foreign students as part of a pressure campaign seeking changes to governance and policies at the Ivy League school.

Administration officials have also cut more than US$2.6 billion in research grants, ended federal contracts and threatened to revoke the tax-exempt status for the school Trump has derided as a hotbed of liberalism.

Harvard sued the Department of Homeland Security in May after the agency withdrew the school’s certification to host foreign students and issue paperwork for their visas.

The action would have forced Harvard’s roughly 7,000 foreign students to transfer or risk being in the United States illegally.

The university called it illegal retaliation for rejecting the White House’s demands to overhaul Harvard policies around campus protests, admissions, hiring and other issues.

Burroughs temporarily had halted the action hours after Harvard sued and then granted an initial injunction on Friday.

The latest injunction came on Monday in response to another move from Trump, who cited a different legal justification when he issued a June 4 proclamation blocking foreign students from entering the United States to attend Harvard.

In her order, Burroughs said the case is about freedom of speech and freedom of thought.

"Here, the government’s misplaced efforts to control a reputable academic institution and squelch diverse viewpoints seemingly because they are, in some instances, opposed to this administration’s own views, threaten these rights," she wrote.

Trump has been warring with Harvard for months after it rejected a series of government demands meant to address conservative complaints that the school has become too liberal and tolerated anti-Jewish harassment. (AFP)