Vice president Joe Biden and the man who wants to succeed him, Republican Paul Ryan, clashed over the Obama administration's policy in Libya and Iran in the opening minutes of a vice presidential debate, with Ryan citing it as evidence that it is weakening America's standing in the world.

It only grew more heated, as the two also sniped at each other over Afghanistan and Syria, as well as the slow economy, taxes and the government health care programme for the elderly.

It was a feisty performance on both sides, with both candidates repeatedly interrupting each other - and the moderator too.

The stakes are not generally this high in vice presidential debates, but Mr Biden was under pressure to undo some of the damage from President Barack Obama's lacklustre debate performance last week against the Republican candidate, Mitt Romney, and to restore energy to the Democratic campaign less than a month before the November 6 election.

The two scrapped seconds into the debate, with Mr Ryan saying the September 11 death of the US ambassador in an attack at the US Consulate in Benghazi was evidence that the administration's foreign policy was unravelling. "That's a bunch of malarkey," Mr Biden retorted twice. The folksy vice president also referred to Mr Ryan's accusations as "a bunch of stuff".

On Iran, Mr Biden defended current sanctions as the toughest ones in history, while Mr Ryan said President Barack Obama has allowed Iran to get four years closer to building a nuclear weapon, and accused the White House of ignoring the warnings of Israeli prime minister Benjamin Netanyahu and not standing up for its chief ally.

The candidates also disagreed on Syria, with Mr Ryan accusing the administration of inaction and saying it was outsourcing foreign policy to the United Nations. Mr Biden said the last thing the US needs is another ground war in the Middle East, and that if Ryan and Romney want to send troops to Syria they should just say so.

The slow economy has been the dominant issue of the US election, and Mr Ryan cited high unemployment numbers as evidence that there is no economic recovery under way. In turn, the pressure was on for Mr Biden to go where Mr Obama did not in his own debate. He quickly did so, citing Mr Romney's opposition to the administration's successful auto industry bailout, and noting that it was not surprising given the Republican's recent videotaped comment in which he was heard saying that 47 percent of Americans view themselves as victims who depend on the government and refuse to take responsibility for their lives.

About 41 states are seen as essentially already decided for Mr Romney or Mr Obama, leaving nine up for grabs, including Ohio. No Republican has ever won the White House without carrying that state.

The 90-minute debate - the only vice presidential one - was moderated by Martha Raddatz, senior foreign affairs correspondent for ABC News. Mr Romney and Mr Obama meet again on Tuesday for a town hall-style debate in Hempstead, New York. Their third and last debate is scheduled for October 22 in Boca Raton, Florida.