US President Barack Obama and his Republican rival Mitt Romney on Monday clashed over economic policies in their third and final face-to-face presidential debate.

Romney attacked Obama's economic records, saying the US economy was not getting stronger under Obama's watch and Obama has not balance the budget of the federal government in nearly four years in office.

"We need a strong economy," said Romney, adding that the mounting debt is the "biggest national security threat" for the nation.

"We have to strengthen our economy here at home. You can't have 23 million people struggling to get a job," Romney charged.

Obama defended his economic records, saying the administration was endeavoring to bring manufacturing jobs back to the United States and to cut the nation's deficit in a balanced way.

The world's largest economy should ensure key investments on education and other areas that were important to US long-term competitiveness, Obama stressed.

The United States should make efforts to develop its own economy, its own energy sectors and its own education system, Obama added.