By the BBC's David Bamford

Reports from Switzerland say a deal on the return to Nigeria of millions of dollars deposited in Swiss banks by the late Nigerian military ruler, General Sani Abacha, has collapsed.

Obasanjo was heavily criticised for negotiating with the Abacha family

Swiss Justice Ministry officials are quoted as saying the deal has fallen through because General Abacha's son, Mohammed, has not signed vital legal papers releasing the money.

The extraordinary out-of-court agreement between Nigeria and General Abacha's bereaved family was reached in May.

It was agreed the general's family could keep $100 million provided that his son signed an agreement enabling foreign banks in Switzerland and elsewhere to return to Nigeria a further $1 billion of allegedly looted money.

Embarrassment

The deal was apparently linked to the release from prison this week of Mohammed Abacha, ending his three-year period behind bars on charges of embezzlement.

Suspicions that the deal might be going awry arose on Wednesday when jubilant Mohammed was quoted as saying that - despite his release - he had made no commitment to sign anything.

Now the increasingly embarrassed Swiss authorities have acknowledged that they have received no signed papers, and therefore are in no position to hand over any of the Abacha family fortune to Nigeria.

Throughout this long affair, Nigerian President Obasanjo has faced a no-win situation.

He was condemned by one side for negotiating any deal with the Abachas.

At the same time, Mr Abacha's supporters slammed the president for detaining the general's son for so long on what they say are spurious charges.