Republican governors in half of the US have backed Texas in an intensifying standoff with the federal government over illegal immigration.

The Supreme Court ruled this week against Texas Governor Greg Abbott, who has strung razor wire along miles of the frontier with Mexico.

But the Republican has vowed to add more razor wire to crack down on what he calls an invasion.

A record 225,000-plus illegal migrants crossed the border in December alone.

On Thursday, 25 Republican governors released a joint statement of solidarity with Mr Abbott for "stepping up to protect American citizens from historic levels of illegal immigrants, deadly drugs like fentanyl, and terrorists entering our country".

The latest border flashpoint focuses on a small stretch of the Rio Grande River that has become one of the busiest spots for migrants crossing illegally from Mexico.

As part of his Operation Lone Star, Mr Abbott has sought to block or deter entry into his state, including by installing about 30 miles (48km) of razor wire barriers along the city of Eagle Pass.

On Monday the Supreme Court handed a victory to the administration of President Joe Biden, a Democrat, in its standoff with Texas.

The justices ruled by 5-4 that US Border Patrol, a federal agency, could cut or clear out the concertina wire set up by the Texas National Guard.

The justice department had argued the fencing hampers the work of Border Patrol agents in that it poses a danger to both migrants and law enforcement. Some of the illegal migrants have cut themselves on the wire.

Appearing on Fox News on Thursday, Mr Abbott said: "Because the Biden administration has really, truly abdicated its responsibility to secure the border and enforce the laws, Texas, very simply, is securing the border."

He has posted photos of the Texas National Guard laying down new razor wire along the river.

The move does not appear to violate the Supreme Court order, which granted permission for the removal of existing wire, while saying nothing about adding new barriers.

Democrats are urging the president to take a tougher stance against Texas.

"Governor Greg Abbott is using the Texas National Guard to obstruct and create chaos at the border," congressman Joaquin Castro wrote on X, calling for federal control over the guardsmen.

Governor Abbott is also facing legal challenges from the Biden White House over his orders to install floating barriers in the Rio Grande and to jail thousands of migrants on trespassing charges.

And, as the governor continues to bus migrants to Democratic cities and states, pressure is mounting on Mr Biden to take drastic action to stem the flow of arrivals.

Last week, Mr Biden said he was "ready to act", but argued lawmakers on Capitol Hill must first agree on significant policy reforms.

The prospects of a grand bargain, however, in either chamber of Congress, let alone both, appear slim.

Republicans in the US House of Representatives are currently leading an effort to impeach and remove the president's top border official, Homeland Secretary Alejandro Mayorkas.

An emerging bipartisan border deal in the US Senate meanwhile faces objections from right and left.

Former President Donald Trump, the Republican White House frontrunner, has reportedly pressured allies to kill the bill to avoid giving Mr Biden a win in an election year.

Immigration is a central issue ahead of the November 2024 general election, with voters in Iowa and New Hampshire delivering primary victories to Mr Trump in part due to their concerns over the border.