President Biden's administration will restart a controversial Trump-era border programme that forces asylum seekers to wait in Mexico for US immigration hearings, in keeping with a federal court order.
US has reluctantly announced plans to accept the Trump-era policy which it again called "deeply flawed" and agreed to Mexico's conditions for resuming it.
Thursday's decision will again make migrants seeking to enter the US to stay in Mexico as they await immigration hearings.
President Joe Biden scrapped the policy, but a lawsuit by Texas and Missouri forced him to put it back into effect, subject to Mexico's acceptance.
Mexico's foreign relations secretary said in light of US concessions Mexico will allow returns, expected to begin next week, "for humanitarian reasons and for temporary stays."
Mexico's conditions include Covid-19 vaccinations for migrants, more protection in dangerous Mexican border cities, better access to attorneys, and quicker resolution of cases.
About 70,000 asylum-seekers have been subject to the policy, which then president Donald Trump introduced in January 2019 and which Biden suspended on his first day in office.
Illegal border crossings fell sharply after Mexico, facing Trump's threat of higher tariffs, acquiesced in 2019 to the policy's rapid expansion.
Asylum-seekers were victims of major violence while waiting in Mexico and faced a slew of legal obstacles, such as access to attorneys and case information.
US acting to comply with court order
Migrants are expected to be returned starting on Monday in one border city, which has not been identified.
It will eventually be done in seven locations: San Diego and Calexico in California; Nogales, Arizona; and the Texas border cities of Brownsville, Eagle Pass, El Paso, and Laredo.
The Homeland Security Department said on Thursday that it was acting to comply with a court order but that secretary Alejandro Mayorkas believes the policy "has endemic flaws, imposed unjustifiable human costs, pulled resources and personnel away from other priority efforts, and failed to address the root causes of irregular migration."
"Deeply flawed," White House spokesman Jen Psaki said on Thursday when describing the policy.
"We're working to implement under the court order," she said.
The policy's new iteration, outlined for reporters by Biden administration officials who spoke on the condition that they not be named, includes major additions and changes that Mexico demanded.
The US will try to complete cases within 180 days, a response to Mexico's concerns that they will languish.