BARACK Obama is refusing to hold talks with his Republican ­opponents over the dispute that has shut down the US Government until the politicians agree to lift their "threats" against the economy.

The President said in a major speech in Washington DC last night that the party, which is using a looming debt limit deadline of October 17 for leverage in the dispute, was committing political "extortion".

The shutdown occurred last week when Congress failed to agree a budget, with Republicans saying they would only agree if major changes were introduced to the President's healthcare law.

Democrats in the Senate also want to permit $1 trillion dollars or more in new borrowing above the current $16.7tn dollar debt ceiling that the administration says will be hit on October 17, but Republicans have said they want spending cuts in exchange.

Mr Obama said any negotiations on the ongoing situation or the looming debt limit "shouldn't require hanging the threats of a shutdown or economic chaos over the heads of the American people".

He also warned of the ­repercussions of defaulting on the nation's financial responsibilities should Congress fail to raise the debt limit.

The prospect of a default has potentially great consequences for the United States and the world. The International Monetary Fund (IMF) lowered its global economic growth forecasts and warned that the US would hurt the global ­economy if it fails to raise its borrowing limit.

At the White House, Mr Obama said he had spoken with Republican House Speaker John Boehner earlier and was "happy to talk with him and other Republicans about anything".

But he said any talks should not depend on hanging the threats of a shutdown over the American people.

Mr Obama said crossing the debt limit could disrupt markets, undermine international confidence in America, permanently increase the nation's borrowing costs and add to its deficits and debt, and pose the "significant risk of a very deep recession".

The US leader also said ­Republicans had yet to offer any serious positions from which to resolve the ongoing political ­gridlock, saying that had instead decided to "run out the clock" in order to "give them more leverage".

On Tuesday, Mr Boehner told reporters he "wanted to have a conversation" with Mr Obama and congressional Democrats.

He said: "I'm not drawing lines in the sand.

"It is time for us to just sit down and resolve our differences."

The US government partially shut down operations on October 1 after Republicans who control the House of Representatives refused to approve a budget.

They said they would only do so if Mr Obama's healthcare reform law was delayed or stripped of funding.

Mr Obama and the Democrats have refused, stressing that the law was passed in 2010, has been approved by the Supreme Court, and was a central issue in the 2012 election which Mr Obama won.

Meanwhile, some 350,000 civilian defence department workers were summoned back to work on Monday as the result of legislation Congress passed and Mr Obama signed after the shutdown began.

Other agencies, such as Nasa and the Environmental Protection Agency, remain mostly closed.

An estimated 450,000 federal employees remain idle at agencies responsible for domestic programmes, ranging from the departments of education to energy, and including labour, health and human services, interior, transportation.