President Barack Obama and Republican rival Mitt Romney prepared for today's third and final presidential debate, which will focus on foreign policy, especially the Middle East and terrorism. It is their last chance to directly confront each other before millions of TV viewers with polls showing the race deadlocked.

The 90-minute debate in Boca Raton, Florida, comes just 15 days before the 6 November election.

While the economy has been the dominant theme of the election, foreign policy has attracted renewed media attention in the aftermath of last month's attack on the US Consulate in Benghazi, Libya, that killed four Americans, including US Ambassador Chris Stevens.

Obama had ranked well with the public on his handling of international issues and in fighting terrorism, especially following the death of Osama bin Laden. But the administration's response to the Libya attack and questions over levels of security at the consulate have given Romney and his Republican allies an issue with which to raise doubts as to Obama's foreign policy leadership.

Romney's team has focused on Libya, following reports that Obama's administration could have known early on that militants, not protesters angry over a film produced in the US that ridiculed Islam, launched the attack that killed the US ambassador there.

Obama has insisted that information about the Libya attack was shared with the American people as it came in.

Breaking news on the eve of the debate includes that Obama's administration is prepared to engage in bilateral discussions with Iran to find a diplomatic settlement to the impasse over Tehran's reported pursuit of nuclear weapons. Iran has been a recurring issue in the presidential election campaign.

Heading into the campaign's final weeks, the economy and other domestic issues remain the main focus of both candidates.

Romney is upping his criticism of Obama's plans for a second term, accusing the Democrat of failing to tell Americans what he would do with four more years. The Obama campaign is aggressively disputing the notion, claiming it is Romney who has failed to provide voters with specific details.

At campaign events, and in a new ad and fundraising appeal out Saturday, Romney is setting up the closing weeks as a choice between what he says is Obama's "small" campaign that is offering little new policy and his own ambitious plan to fundamentally change America's tax code and entitlement programmes.

The new Romney ad criticises the president's policies on debt, health care, taxes, and energy, arguing that Obama is simply offering more of the same. The fundraising appeal hits Obama for raising taxes and increasing the debt by $5.5 trillion, repeating the lack-of-agenda criticism.

Obama's campaign disputes the notion that the president hasn't outlined a detailed second-term agenda, pointing to his calls for immigration reform, ending tax breaks for upper income earners, fully implementing his health care overhaul and ending the war in Afghanistan.

Obama, at the Democratic National Convention, called for creating one million manufacturing jobs over the next four years, with a mix of corporate tax rate cuts and innovation and training programmes. He has set a goal of cutting the growth of college tuition in half over the next 10 years. He has also called for Congress to pass proposals he made last year, which include tax credits for companies that hire new workers and funding for local municipalities to hire more teachers, police officers and firefighters.

The president's aides are particularly irked by the questions about Obama's second-term agenda, because they say it's Romney who has failed to provide voters with details as to his plans. They point to Romney's refusal to provide specifics about his tax plan or outline what he would replace the president's health care overhaul with if he makes good on his promise to repeal the federal law.

The Obama campaign has also stressed that it is hard to predict what Romney might do as president, since he has changed his positions on many issues.

The presidency is decided in state-by-state contests, not by a national popular vote. Forty-one of the 50 states are essentially already decided, and the candidates have taken the fight to the remaining nine, which include Ohio and Florida.