The Presidential candidate Barack Obama is increasing his lead over John McCain as the US presidential election campaign enters its final phase, according to a poll published by the Washington Post.

It said 53 per cent of the electorate would vote for Obama, compared to 44 per cent for McCain. Barack Obama also led in several key states seen as decisive in next Tuesday's election.

John McCain campaign manager Rick Davis predicted a 'comeback' in the final days, as both sides ramped up their advertising and volunteer operations.

Davis said the Republican campaign expected to outspend Barack Obama in the final week by more than 10 million $, which would turn the tables on the trend of the last few months.

Obama and McCain were geared up for a final weekend of campaigning, volunteering and television advertisements, as voters turned out in droves to cast their ballots early.

Both campaigns claimed an edge in the early voting stakes in key battlegrounds including Florida, Nevada, New Mexico and North Carolina, as well as absentee ballots cast in other states.

David Plouffe, the campaign manager of Democratic nominee Obama, claimed more than 40 per cent of the total expected voters had already cast ballots in states that allow early voting. Higher turnout historically helps Democrats in presidential elections.

The two candidates continued to make stops Friday through a handful of swing states. On Monday, McCain plans rallies in seven different states.

Obama has raised unprecedented amounts in donations through the course of the presidential campaign - more than 600 million dollars - but a spending spree over the last two months across the country may have left Republicans with an opening in the final stretch.

But Plouffe announced that Obama's campaign would begin advertising in McCain's home state of Arizona, as well as North Dakota and Georgia - a sign of just how far Obama is trying to push into traditional Republican territory.