Media playback is unsupported on your device Media caption Mitt Romney says the president seems to be running "just to hang on to power"

Republican presidential candidate Mitt Romney has branded the Obama campaign as one of "division and attack and hatred", in a national TV interview.

Speaking to CBS News, Mr Romney said President Barack Obama was "running just to hang on to power".

His criticism followed an acrimonious day on the campaign trail, which saw the Romney and Obama camps spar over healthcare and Wall Street.

Mr Romney is challenging Mr Obama for the White House in November's election.

'Divisive effort'

Recent opinion polls show the candidates locked in a close race, with Mr Obama maintaining a narrow lead over his opponent.

It is a striking feature of American political debate that for some, any mention of race is on the index of forbidden topics

Correspondents say the intensity of negative attacks seems to have stepped up a gear since Mr Romney announced Wisconsin Representative Paul Ryan as his vice-presidential pick on Saturday.

Mr Romney told CBS News that the Democratic president was "running just to hang on to power, and I think he would do anything in his power" to stay in office.

But an Obama campaign spokeswoman responded that Mr Romney's comments seemed "unhinged".

The exchange came a day after Vice-President Joe Biden told a mostly black audience in rural southern Virginia that, if elected, Mr Romney would "unchain Wall Street".

"They're going to put y'all back in chains," Mr Biden said.

In Wednesday's interview, Mr Romney said: 'I can't speak for anybody else, but I can say that I think the comments of the vice-president were one more example of a divisive effort to keep from talking about the issues."

Media playback is unsupported on your device Media caption The BBC analyses Republican running mate Paul Ryan's controversial economic policy

He added that he did not intend to deregulate the financial industry. "Of course, we have to have regulation on Wall Street and on every street to make sure that our economy works well, so it's factually inaccurate to begin with," Mr Romney said.

Negative advertising has accompanied the barbs traded on the campaign trail.

Last week, a group supporting Mr Obama released a video effectively blaming Mr Romney for a woman's death.

In the ad, a former steel plant worker recalled how his wife's cancer could not be treated after he lost his health insurance when Bain Capital, the private equity firm Mr Romney once led, shut his factory.

On Wednesday, Mr Obama continued campaigning in Iowa, on the third and last day of a bus tour through the state. Mr Romney is attending fundraisers in North Carolina and Alabama.

Meanwhile, Mr Ryan is due to campaign in Ohio and Mr Biden is scheduled to appear at campaign events in Virginia.