Media playback is unsupported on your device Media caption President Obama: "My expectation is if you want to be president, you've got to work for everybody, not just for some" (Video: Worldwide Pants)

President Barack Obama has criticised Republican rival Mitt Romney, saying that anyone running for the White House needs to work for all Americans.

Mr Obama told chat show host David Letterman Mr Romney was wrong to describe 47% of Americans as "victims".

Earlier, Mr Romney defended his remarks after secretly filmed video of a speech to donors became public.

He told Fox News he knew those "dependent on government" would not vote for him in November's election.

Mr Romney also decried the notion of government "redistribution", calling it an "entirely foreign concept".

More leaked video emerged on Tuesday, showing Mr Romney saying Palestinians do not want peace in the Middle East.

At the very time when the opinion polls suggests that he needs to be aggressively fighting for every inch of ground, he has lost the microphone

The full video of the Florida fundraiser was also published by liberal investigative magazine Mother Jones.

In Tuesday's Fox interview, Mr Romney stood by his comments about the 47% of Americans who do not pay income tax. He said they support President Barack Obama and would never vote for him. He said his statement was "about the campaign".

"I'm talking about a perspective of individuals who are not likely to support me," he said. "Those that are dependent on government and those that think government's job is to redistribute, I'm not going to get them," Mr Romney said.

Media playback is unsupported on your device Media caption Romney's views on the Middle East prompted criticism from Palestinians. Video: www.motherjones.com

The Republican says he expects Mr Obama to receive about half of the vote in the November election because of these voters.

The real problem, he added, was that so many people were not eligible to pay income tax because they had fallen into poverty.

Recent polls indicate that the election is likely to be a close contest, although an NBC News/Wall Street Journal poll released on Tuesday evening showed that Mr Obama's approval rating has hit 50% for the first time since March.

In addition, the poll put the president ahead of Mr Romney by 5% among likely voters polled across the nation. The poll had a 3.6% margin of error.

'Israel's destruction'

On Mr Letterman's show, Mr Obama said he told the US on election night in 2008 he would work for everyone, including those who did not vote for them.

"One thing I've learnt as president is you represent the entire country," he said.

Who pays US income tax? The US federal government runs off two kinds of taxes: payroll taxes, which fund benefits such as Social Security, and income taxes, which largely fund the rest of the federal budget. In 2011, the Tax Policy Center studied the tax liability of US households: 53.6% paid income taxes, 46.4% did not

28.3% paid payroll taxes but not income taxes

10.3% were elderly and retired and were not taxed on Social Security benefits

6.9% did not pay any tax with household incomes of less than $20,000 (£12,300) The majority of those who pay payroll but not income tax do so because of tax benefits for the elderly, families with children and low-income earners.

"There are not a lot of people out there who think they are victims" or simply entitled to benefits, Mr Obama said.

The president's rebuke came at the end of a day in which more clips of Mr Romney's fundraising address emerged. In one, Mr Romney said the Palestinians are "committed to Israel's destruction".

"The Palestinians have no interest whatsoever in establishing peace," he says in the video, adding that "the pathway to peace is almost unthinkable to accomplish".

But chief Palestinian negotiator Saeb Erekat told Reuters news agency that Mr Romney was wrong to accuse the Palestinians of not seeking peace.

"Only those who want to maintain the Israeli occupation will claim the Palestinians are not interested in peace," he said.

In another clip, the former Massachusetts governor is shown discussing Iran's nuclear programme, and warning that America itself could come under attack.

$50,000-a-head fundraiser

The first clips released on Monday showed the Republican candidate saying those who did not pay income tax would never vote for him.

"There are 47% who are with him [Mr Obama], who are dependent upon government, who believe that they are victims, who believe the government has a responsibility to care for them, who believe that they are entitled to healthcare, to food, to housing, to you-name-it," he said.

Media playback is unsupported on your device Media caption Mitt Romney: "They'll vote for this president no matter what" Video: www.motherjones.com

Mr Romney said in the video that his role "is not to worry about those people. I'll never convince them they should take personal responsibility and care for their lives."

The video clips provided to Mother Jones are said to have been filmed at a $50,000 (£31,000) per head fundraiser in May.

Earlier this week, the Romney campaign announced a new shift in strategy after several difficult days for the candidate.

Campaign advisers told US media on Monday that the Republican would speak more specifically about his budget plans and tax policy.