The U.S. presidential candidates are heading into the final two days of campaigning with the outcome still too close to call, BBC News reported.

Republican Mitt Romney will campaign in Iowa, Ohio, Pennsylvania and Virginia, while Barack Obama heads for New Hampshire, Florida, Ohio and Colorado.

Both candidates addressed large rallies on Saturday, Nov 3 in key swing states.

The latest ABC News/Washington Post survey suggests the pair are level with 48% of support.

Both Mr Obama and Mr Romney are showing signs of exhaustion as they continue their daily, multiple-state visits to attract any undecided voters in the marginal battleground states that will determine the winner.

Mitt Romney: ''I can't wait to get started''

Former President Bill Clinton was also suffering as he joined Mr Obama in Virginia, addressing the rally in hoarse tones, saying he had "given my voice in the service of my president".