President Barack Obama accused Republican challenger Mitt Romney of sending mixed messages with his foreign policy proposals on the Middle East and Russia on Monday in their third and final debate.

Seeking to gain an advantage with polls showing a tied race, Obama and Romney clashed from the start of their debate. Obama said that the Republican presidential candidate, by declaring Russia a "geopolitical foe" of the United States, was seeking to return the United States to a long-abandoned Cold War stance.

"The Cold War has been over for 20 years," said Obama, turning to Romney as they sat at a table before moderator Bob Schieffer. "When it comes to your foreign policy, you seem to want to import the foreign policies of the 1980s."

Romney, wanting to make no mistakes that could blunt his recent surge, said Obama's policies toward the Middle East and North Africa were not stopping a resurgence of the threat from al Qaeda in the region.

"Attacking me is not an agenda," said Romney. "Attacking me is not how we deal with the challenges of the Middle East."

He noted he had also called the nuclear challenge from Iran the greatest national security threat to the United States.

Romney also criticized Obama for an open-microphone comment he made to then-Russian President Dmitry Medvedev that he would have more "flexiblity" after America's Nov 6 election.

Instead of showing Russian President Vladimir Putin more flexibility, Romney said, "I'll give him more backbone."

The debate was the last major opportunity for either candidate to appeal directly to millions of voters - especially the roughly 20 percent who have yet to make up their minds or who could still switch their support at the Nov. 6 election.

World hot spots like Libya and Iran figured prominently, with Romney seeking to put pressure on Obama over what the Republican considers weak responses to the killing of the U.S. ambassador to Libya on Sept. 11 and Iran's nuclear ambitions.

The two candidates were tied at 46 percent each in the Reuters/Ipsos online daily tracking poll. Other surveys show a similar picture.

Obama came to Boca Raton with the advantage of having led US national security and foreign affairs for the past 3 1/2 years. He gets credit for ending the Iraq war and the killing of al Qaeda leader Osama bin Laden in 2011.

But Romney will have many opportunities to steer the conversation back toward the weak US economy, a topic on which voters see him as more credible. His goal was to appear as a credible alternative to Obama and avoid any gaffes that could deflate his recent surge.

Presidential debates have not always been consequential, but they have had an impact this year.

Romney's strong performance in the first debate in Denver on Oct. 3 helped him recover from a series of stumbles and wiped out Obama's advantage in opinion polls.

Obama fared better in their second encounter on Oct. 16, in what was deemed to be one of the most confrontational presidential debates ever, but that has not helped him regain the lead.