The border wall between the US and Mexico is seen in San Diego, the United States, April 30, 2018. (Xinhua/Huang Heng)

The US on Wednesday began returning migrants to the Mexican city of Tijuana in a restart of a Trump-era program that forces asylum seekers to wait for US court hearings in Mexico, Mexican authorities and the UN migration agency said.

The US and Mexico in December  2021 agreed to relaunch the controversial scheme known as Migrant Protection Protocols (MPP), in keeping with a US federal court order.

US President Joe Biden, a Democrat, has struggled to reverse many hardline immigration policies put in place by his Republican predecessor, Donald Trump.

Biden ended MPP soon after his inauguration in January as he sought to pursue what he called a more humane approach to immigration. But a federal judge ruled Biden's move did not follow proper procedure, and in August ordered MPP reinstated.

The program first resumed in December at the international crossing connecting El Paso, Texas, to Ciudad Juarez. More than 200 people have been returned to Mexico so far under the relaunch of MPP, according to the UN's International Organization of Migration (OIM). Two migrants were returned to Tijuana, across from California, on Wednesday with future appointments in US courts, an official with OIM told Reuters. The migrant rights advocacy group Al Otro Lado told Reuters the two men were Colombian nationals.

Neither US Customs and Border Protection (CBP) nor Mexico's immigration agency immediately responded to requests for comment.

The UN's refugee agency and advocacy groups have criticized the restart of the Trump-era policy, warning migrants face the risk of kidnapping, rape, and extortion in dangerous Mexican border towns.