The United Nations on Thursday called for a tax on billionaires to help raise more than $400 billion a year for poor countries.

An annual lump sum payment by the super-rich is one of a host of measures including a tax on carbon dioxide emissions, currency exchanges or financial transactions proposed in a UN report that accuses wealthy nations of breaking promises to step up aid for the less fortunate.

The annual World Economic and Social Survey says it is critical to find new ways to help the world's poor as pledged cash fails to flow.

The report estimates that the number of people around the globe worth at least $1 billion rose to 1,226 in 2012.

There are an estimated 425 billionaires in the United States, 315 in the Asia-Pacific region, 310 in Europe, 90 in other North and South American countries and 86 in Africa and the Middle East.

Together they own an estimated $4.6 trillion so a one percent tax on their wealth would raise more than $46 billion, according to the report.

"Would this hurt them?" it questioned.

"The 'average' billionaire would own $3.7 billion after paying the tax. If that billionaire spent $1,000 per day, it would take him or her over 10,000 years to spend all his or her wealth," the report says.

It says that the wealth of billionaires grew at an average rate of four percent a year in the two decades before the 2008-2009 financial crisis.

"If that rate of growth returned with no wealth tax, the average billionaire's wealth would double in less than 18 years."

The idea could appeal to the likes of Warren Buffett, the US tycoon who has complained that he pays a lower tax rate than his secretary. France's new Socialist government has caused consternation by vowing a 75 percent tax on salaries above one million euros ($1.24 million).

But the UN acknowledged that the idea is unlikely to get widespread support from the target group, saying that for now its tax on the unimaginably wealthy remains "an intriguing possibility."

"It has not been regarded as a means of raising revenues for international cooperation," the report says.

The document gives other ideas for international taxes, including:

-- a tax of $25 per tonne on carbon dioxide emissions would raise about $250 billion. It could be collected by national governments, but allocated to international cooperation.

-- a tax of 0.005 percent on all currency transactions in the dollar, yen, euro and pound sterling could raise $40 billion a year.

-- taking a portion of a proposed European Union tax on financial transactions for international cooperation. The tax is expected to raise more than $70 billion a year.

It also suggests expanding a levy on air tickets that a number of nations already impose to raise money for drugs for poor states through UNITAID, a UN initiative.

The report says more than $1 billion has been handed over to UNITAID since the levy started in 2006.