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US President Barack Obama has urged Congress to take action to avoid deep spending cuts due to begin on Friday.

Speaking at a shipyard in the state of Virginia, he warned the defence industry would be hit especially hard.

The US Navy has already told suppliers it would be forced to cancel future contracts if the cuts go through.

The US immigration and customs agency has meanwhile begun to release illegal immigrants from jails, as a result of the looming budget cuts.

Noting current "fiscal uncertainty", the US Immigration and Customs Enforcement agency said hundreds of illegal immigrants had been "placed on an appropriate, more cost-effective form of supervised release".

On Monday, Homeland Security Secretary Janet Napolitano warned the cuts would hit her department's core programmes - including border and airport security.

Firing a shot across lawmakers' bows, Mr Obama said the $85bn (£56bn) cuts, known as the sequester, were "arbitrary" and "dumb".

"They are a self-inflicted wound that doesn't have to happen," he said, speaking to shipbuilders gathered for his speech.

He delivered his remarks standing in front of a submarine propeller at the shipyard where scheduled maintenance on the aircraft carrier USS Abraham Lincoln has been delayed due to the cuts.

Mr Obama blamed Republican lawmakers for failing to compromise, and for rejecting some revenue increases to soften the blow of the cuts.

He added: "There are too many Republicans in Congress right now who refuse to compromise even an inch when it comes to closing tax loopholes and special interest tax breaks."

Tuesday's event was the president's latest effort in a campaign to sell to the American public his plan to avoid the sequester.

"I need you, Virginia, to keep up the pressure," the president said. "If you stand up and speak out, Congress will listen.

Unusually, Mr Obama, a Democrat, was accompanied on Tuesday by a Republican congressman, Scott Rigell, who fears job losses in his Virginia constituency if the cuts take effect.

Both Democrats and Republicans agreed to the sequester in 2011 as part of a bill to raise the US debt ceiling - the legal limit the government can borrow.

The cuts were designed to be so unappealing that lawmakers would be forced to agree to a separate deal, but amid gridlock in Washington, such an agreement was never reached.

Some Republicans have been saying the president is exaggerating the negative consequences of sequestration.

House Speaker John Boehner accused Mr Obama of using "our military men and women as a prop in yet another campaign rally to support his tax hikes".

The top Republican in the Senate, Mitch McConnell, said: "The president's been running around acting like the world's going to end because Congress might actually follow through on an idea he proposed and signed into law."

As well as the homeland security secretary, other Obama cabinet members have warned of dire consequences if the sequester is not stopped.

Last week, Education Secretary Arne Duncan said teachers' layoffs have already begun - although no details have been released.

Interior Secretary Ken Salazar said US national parks would face a "perfect storm" if the sequester takes effect.

And Transport Secretary Ray LaHood suggested air traffic controllers would be furloughed while air travel could face delays.