The US president Barack Obama and Republican challenger Mitt Romney have traded words and accused each other for lacking a clear vision on foreign policy at the third and final presidential debate in Florida.

"I know you haven't been in a position to actually execute foreign policy, but every time you've offered an opinion, you've been wrong," said Obama who looked aggressive in the beginning of the debate.

Romney criticised Obama in handling the unrest in Middle East and the growing threat of extremism in North Africa.

Romney said the disturbing events of the Middle East present "a pretty dramatic reversal in the kinds of hopes we had for that region".

The third and last in the series of televised presidential debates saw Romney agreeing to some of the foreign policy decisions of the president such as the drone attacks in Pakistan and the killing of Osama bin Laden.

"It's widely reported that drones are being used in drone strikes, and I support that... entirely and feel the president was right to up the usage of that technology," said Romney.

United States should "continue to go after the people that represent a threat to this nation and to our friends".

On eliminating the al-Qaida leader, Romney said: "I congratulate him on taking out Osama bin Laden and taking on the leadership of al-Qaida.

But we can't kill our way out of this... We must have a comprehensive strategy".

The final debate moderated by CBS News' veteran presenter Bob Schieffer did not see any catchy one liners or quick wits except Obama's comment on Romney's calls for inclusion of more ships built by the US Navy in the military.

Romney said United States should typically have 300 and only had 285, to which Obama responded: "Governor, we also have fewer horses and bayonets," evoking laughter among the audience.

Polls after the debate gave Obama a narrow edge over his rival presidential candidate. A CNN/ ORC International poll of debate viewers gave 48 percent and 40 percent for Obama and Romney respectively with a margin of error of plus or minus 4.5 percentage points.

In a CBS News poll of 521 undecided voters, Obama emerged winner with 53 percent and 23 percent for Romney with a margin of error of 4 points.

Scroll through the pictures to have a glimpse of two presidential hopefuls during the debate at the Lynn University, Boca Raton, Florida.