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Joe Biden has walked along the US-Mexico border in Texas to see up close one of his presidency's biggest issues.

He visited a migrant centre in El Paso and joined Border Patrol agents in touring a section of the border wall.

The number of migrant crossings has spiralled in recent months, making the Democratic president vulnerable to the accusation he is soft on security.

Last week he announced tougher measures to expand the nationalities of those who can be sent back to Mexico.

But that left the Republican governor of Texas, Greg Abbott, unimpressed - he said the president was failing to enforce immigration laws.

"You have violated your constitutional obligation to defend the States against invasion through faithful execution of federal laws," he wrote in a letter which he handed to the president upon his arrival.

The governor's party said it intends to use its newly acquired control of the House of Representatives to investigate the Biden administration's handling of immigration.

Mr Biden's visit, his first since becoming president two years ago, was also expected to include meetings with border officials to discuss migration and the increased trafficking of fentanyl and other opioids.

El Paso, on the south-west edge of Texas, is one of the most common crossing points, often used by Nicaraguans fleeing repression, crime and poverty in their country.

A controversial Trump-era policy that enabled the rapid expulsion of illegal border crossers was due to expire in December but kept in place by a Supreme Court ruling after an outcry from Republicans.