About 20 miles (32km) will be built in Starr County along its border with Mexico, where officials report high numbers of crossings.

Building a border wall was a signature policy of Donald Trump as president and fiercely opposed by Democrats.

In 2020, Mr Biden promised he would not build another foot of wall if elected.

His administration passed a proclamation soon after taking office that said building a wall across the southern border “is not a serious policy solution”.

On Thursday, however, Mr Biden said he “can’t stop” the construction of the border wall because the funding for it had already been appropriated.

When asked whether he believes the wall could work, he replied simply: “no”.

In a statement to Associated News on Wednesday night, the US Customs and Border Protection (CBP) similarly defended the latest move, saying it was using funds already allocated for a border barrier.

“Congress appropriated fiscal year 2019 funds for the construction of border barrier in the Rio Grande Valley, and DHS is required to use those funds for their appropriated purpose,” the statement said.

Mr Biden and the statements stand in stark contrast to a notice about the project on the US Federal Registry in which Homeland Security Secretary Alejandro Mayorkas said that there is “presently an acute and immediate need to construct physical barriers and roads in the vicinity of the border of the United States in order to prevent unlawful entries into the United States in the project areas”.

Speaking at his daily news conference, Mexican President Andrés Manuel López Obrador criticised the announcement, saying that a wall is “contrary” to what President Biden had previously advocated.

“I understand there is strong pressure from extreme right-wing political groups in the United States,” he added.

The rising number of illegal border crossings has made the issue a vulnerable one for president Biden.

More than 245,000 crossings have been made this year in the Rio Grande Valley area alone, government data shows, and September is expected to be a record month.

Several US cities say they are feeling the strain of the influx.

New York City Mayor Eric Adams predicted the cost of housing the more than 100,000 new arrivals since last year will rise to $12bn over the next three years.

Mr Adams is travelling to Mexico, Colombia and Ecuador this week to discourage migrants from setting out. “We are at capacity,” he said on Tuesday.

Source: BBC