Ferdinand Marcos was among those who squirreled away dirty money

The joint UN-World Bank scheme aims to foster relations between developed and developing nations to ensure assets are returned to their rightful owners.

The World Bank says the campaign is a warning to corrupt leaders everywhere.

Switzerland has, so far, been famous for its secretive banks and a relaxed attitude to dirty money, observers say.

Clear message

Swiss banks provided a cosy home for $500m (£249m) looted by former Philippines dictator Ferdinand Marcos, says the BBC's Imogen Foulkes in Berne.

When the Philippines gained a democratic government, it took 18 years to retrieve that money.

Nigeria's former leader Sani Abacha also held $700m (£348m) in Swiss banks.

Switzerland is probably the worst place in the world now for anybody who wants to stack illegal money in a hidden bank account

Paul Seger

Swiss foreign ministry

The new initiative aims to make it easier for developing countries to recover money they often need badly.

By joining the campaign so quickly, Switzerland is keen to send the message that looted assets will not find a home there any longer, says Paul Seger, head of international public law at the Swiss foreign ministry.

"We do not want our financial centre being used by illegal money, and we have really developed quite an extensive framework to prevent such money from coming into Switzerland," he said.

"If it comes to restitute this money as quickly as possible - we have returned in the past years $1.6bn (£795m), which is far more than any other financial place in Europe or elsewhere."

'Fighting a cliche'

Mr Seger says the image of Swiss banks as easy places to hide cash will be hard to shake, despite new laws against money laundering.

"If you look at the last James Bond movie, or Dan Brown's Da Vinci Code, there's always the mean Swiss bankers who hide all this money," he said.

"So we are fighting against a cliche but I think, really, we are fighting it successfully.

"Dictators who have put their money into Swiss bank accounts illegally will now think twice whether they will still do that in the future.

"I would say now that Switzerland is probably the worst place in the world now for anybody who wants to stack illegal money in a hidden bank account."

Switzerland, which once insisted that its banks could do no wrong, has now promised to provide support and expertise to an international campaign to make sure looted assets do not disappear for good, our correspondent says.