Obama kicks off campaign in Ohio and Virginia

Barack Obama has launched his re-election campaign in Columbus, Ohio, a major swing state that could be key to his hopes of winning November's election.

The US president said on Saturday that Democrats would win the election the "old-fashioned way" and that his team would campaign "door by door, block by block, neighbourhood by neighbourhood".

Obama will likely be challenged by Mitt Romney, the former governor of Massachusetts who is on track to gain the 1,144 delegates needed to secure the Republican nomination.

The president used his first political rally to attack Romney for learning the "wrong lessons" as a CEO and promised to move the US economy forward if he wins a second term.

He hit out at his rival Romney, saying the Republican challenger would "turn back the clock".

But he also acknowledged that the 6 November vote would be tight.

He said he understood that many in the country are dissatisfied with the slow pace of the change he promised when he came to power.

On Friday, Obama fended off criticism from Romney over disappointing job figures. The jobless rate in the US has been stuck above 8% since early 2009.

Official figures showed that the US economy created 115,000 jobs during April, down on the previous month and fewer than analysts had expected.

President Obama strolled on stage in Columbus, Ohio, to cheers and chanting from thousands of supporters already warmed up by glitzy campaign videos and an introduction from his wife Michelle.

Ohio and Virginia, could be pivotal states in the November 6 election.

Obama formally launched his Chicago-based re-election effort last year, but his official political events have been confined to fundraisers since then.

Earlier in his weekly address, Obama called for renewed focus on "nation-building here at home" after a decade of US-led war in Afghanistan.

Obama recapped his trip earlier to the central Asian nation, where he signed a strategic partnership agreement with his Afghan counterpart, Hamid Karzai, and marked the anniversary of the killing of Osama bin Laden.