Washington DC - President Donald Trump has halted arrivals of refugees already cleared to enter the US, according to a memo seen Wednesday, as he quickly pursues a sweeping crackdown on migration.

Following an executive order signed Monday hours after Trump took office, "all previously scheduled travel of refugees to the United States is being canceled," said a State Department email to groups working with new arrivals.

The memo asked the UN International Organization for Migration not to move refugees to transit centers and said that all processing on cases has also been suspended.

Refugees already resettled in the US will continue to receive services as planned, it said.

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Trump in each of his presidential campaigns has run on promises to crack down on undocumented immigration.

But the refugee move also targets a legal pathway for people fleeing wars, persecution or disasters.

In his executive order, he said he was suspending refugee admissions as of January 27 and ordered a report on how to change the program, in part by giving "greater involvement" to states and local jurisdictions.

It also revoked his predecessor Joe Biden's decision to consider the impact of climate change in refugee admissions.

New Secretary of State Marco Rubio, the son of Cuban immigrants, said Wednesday that the State Department will "no longer undertake any activities that facilitate or encourage mass migration. "

"Our diplomatic relations with other countries, particularly in the Western Hemisphere, will prioritize securing America's borders, stopping illegal and destabilizing migration and negotiating the repatriation of illegal immigrants," Rubio said in a statement.

Biden had embraced the refugee program as a way to support people in need through legal means.

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In the 2024 fiscal year, more than 100,000 refugees resettled in the US, the most in three decades.

The Democratic Republic of Congo and Myanmar have been among the top sources of refugees in recent years.

Senator Jeanne Shaheen, the top Democrat on the Senate Foreign Relations Committee, voiced alarm at Trump's moves and said that acceptance of refugees was "a core American value."

"The US Refugee Admissions Program has a long history of bipartisan support and is a life-saving tool for the most vulnerable refugees, all while making Americans safer by promoting stability around the world," she said.

The State Department memo said that Afghans who worked with the US until the collapse of the Western-backed government in 2021 could still arrive through their separate resettlement program. But Shaheen voiced concern that Afghans were also being left in limbo with flights cancelled.