A new US border plan risks undermining fundamental international human rights and refugee law, the UN rights chief warned Wednesday.

"The right to seek asylum is a human right, no matter a person's origin, immigration status, nor how they arrived at an international border," the United Nations' High Commissioner for Human Rights Volker Turk said.

Last week, US President Joe Biden announced a new plan to expand the controversial policy known as Title 42, allowing the immediate rejection of people showing up at the border without clearance.

The plan permits the fast-track expulsion to Mexico of some 30,000 Venezuelans, Nicaraguans, Cubans, and Haitians each month.

"These measures appear to be at variance with the prohibition of collective expulsion and the principle of non-refoulement," Turk warned.

Read: Title 42 applies to all migrants into the US, but not Ukrainians

The international principle of non-refoulement guarantees that no individual should be sent back to a country where they would face torture or cruel, inhuman or degrading treatment.

Even before the expansion, "Title 42 has already been used by US immigration officials some 2.5 million times at the southern border to expel people to Mexico or their home country without an individualized assessment of all their protection needs accompanied by due process and procedural safeguards," the UN rights office pointed out.

The White House has said it hopes the new tough plan will stem numbers of migrant and asylum seekers arriving after dangerous journeys organized by smugglers.

To try to appease criticism on the left, Biden said up to 30,000 qualifying migrants will be permitted each month into the US from Venezuela, Cuba, Haiti, and Nicaragua after having applied in their home countries. They need to have a US sponsor and undergo background checks.

Read: Immigrant deportation soar by 29% in 2022, amounting to 4.7 million

The UN rights chief welcomed "measures to create and expand safe and regular pathways."

However, he said that such initiatives should not come at the expense of fundamental human rights, including the right to seek asylum and the right to an individual assessment of protection needs.

Turk also expressed concern about individuals who are most in need of asylum and those in vulnerable situations, saying they were unlikely to meet the restrictive requirements for humanitarian parole, including having a financial sponsor in the US.

He reiterated his call for refugees' and migrants' rights to be respected and protected at international borders.

"We hear a great deal of talk about migration crises, but in reality, it is those migrating who often are the ones truly in crisis," Turk pointed out.

"Rather than vilifying them and stripping them of long-recognised rights, we should be seeking to govern migration humanely and safely with full respect for the human rights of every individual."