Swiss banks have agreed to give back to Nigeria more than half a billion dollars looted from the country by late dictator Sani Abacha and hidden in their vaults.

The $535m tranche - $70m has already been sent back - forms part of a $1bn package being returned by a number of countries.

The deal was reached at a meeting in Geneva on Tuesday, involving officials from the UK, Jersey, Liechtenstein, Luxembourg and Switzerland as well as Nigeria and the Abacha family.

"The largest part of the Abacha assets blocked in foreign countries, in excess of $1bn, are to be transferred to the Bank for International Settlemetnts in Basel, in favour of the Nigerian government," the Swiss Federal Justice Department said in a statement.

General Abacha died of a suspected heart attack in 1998 after a five-year rule during which, the Nigerian government says, he and his family stole more than $3bn.

In doing so, he was carrying on a decades-long tradition of brazen theft of the oil revenues on which the public budget relies, a habit indulged in by almost every one of the dictators who ruled Nigeria for almost all its existence since independence in 1960.

Red faces

While Switzerland has frozen $670m in total, UK banks have been found with much more dirty money - as much as $1.3bn - in their coffers.

Both countries were embarrassed by the 1999 discoveries.

Switzerland had enacted new rules in 1998, only to have the chief investigator resign because he claimed he was being starved of the resources to do the job properly.

The UK authorities and banks, meanwhile, were found to have been even less co-operative than the Swiss - despite the latter's long and sullied reputation for protecting allegedly stolen assets.

And according to the Swiss, at least a third of the money that eventually found its way there had already passed through banks in the UK, US and Austria.

Another $100m or so has been traced to Luxembourg and Jersey, also traditional havens for private banking.

Family ties

The Swiss Federal Justice Department said Abacha's family will get to keep $100m.

That, it said, was acquired prior to Mr Abacha's term of office and according to the Nigerian government "demonstrably does not derive from criminal acts".

The family - which put much of the money into accounts under names very similar to their own, making investigators' lives much easier - has fought hard to hang on to the money, with lawsuits in a number of countries holding up the return of the money.

But it has not got off scot-free, however.

One of Mr Abacha's sons, Mohammed, has been in jail in Lagos since 1999 facing murder charges.