US President Barack Obama has made his final rallying call, to help win crucial battleground states. Joined by former US President Bill Clinton at an outdoor rally in New Hampshire, Obama urged supporters to give his administration a chance to complete its work.

Obama says, "We've made real progress these past four years but New Hampshire, we're here because we know we've got more work to do. As long as there's a single American who wants a job but can't find one, our work is not yet done.

As long as there are families who are working harder and harder but still falling behind, our work is not yet done, as long as there is a child anywhere in New Hampshire, anywhere in this country, who is languishing in poverty and barred from opportunity, our fight has to go on. Our fight has to go on."

Latest polls show New Hampshire is virtually tied between the two candidates. Obama attacked his Republican rival Mitt Romney, saying he won't be able to deliver his promises.

Obama is due to hold rallies in Florida, Ohio and Colorado on Sunday. All three states could help decide the outcome of Tuesday's election. Meanwhile, Mitt Romney spent Sunday morning in Iowa, another of the key battleground states.

He also went on the attack, saying Obama's first term had been marked by broken promises and empty rhetoric.