The case, filed last week in New York State Supreme Court by Ahmad Hamad Algosaibi and Bros (AHAB), is part of running dispute and responds to an earlier complaint filed against AHAB by Mashreq, a Dubai-based bank.

Mashreq Bank, one of the United Arab Emirates' largest, is cited as a "relevant person" in the case.

The charges broke open a dispute between the two groups and numerous regional and international banks that had simmered behind the scenes for two months.

Khobar businesses

At the centre of the scandal are AHAB and al-Sanea's Saad group, closely linked diversified businesses based in the eastern Saudi industrial city of Khobar.

Al-Sanea is married to the daughter of one of AHAB's founders, Abdelaziz Algosaibi.

While the Algosaibi family is an older, well-established trading, industrial and investment group, al-Sanea and his Saad group grew to prominence only in the past 10 to 15 years.

Through extensive international investments he earned his way onto the Forbes global billionaires list, with a fortune estimated earlier this year at $7bn.

"It appears that this fortune was funded in a significant part by funds fraudulently siphoned from AHAB," the Algosaibi complaint alleged.

'Extortionate rates'

Al-Sanea ran the the Money Exchange, the AHAB unit where the suspect deals originated and which normally processes foreign workers' remittances.

According to AHAB's case, since 2005 al-Sanea arranged billions of dollars in foreign exchange deals carrying "extortionate rates" with other banks through the unit.

It says that Mashreq sued it for $150m that it does not owe. It says that if the conglomerate does owe the money, then it is because al-Sanea created the liability through fraud.

"AHAB learned that its former employee, Maan Al Sanea, organised a fraud in which he, among other things, entered into certain transactions in order to engineer the receipt of funds into accounts in the name of AHAB, which he then diverted to his own use," the court document said.

Mashreq, it said, was one of the main partners in the deals, which were hidden from AHAB's management, in part by using forged documents.

"For four years, literally billions of dollars sluiced back and forth between Mashreq and AHAB, all highly unusual transactions on non-commercial terms," the allegations say.

"These transactions could not have served any legitimate commercial purpose."

Company reactions

A representative of Algosaibi declined comment and a London-based spokesman for the Saad group said the company had not been served with the claim.

"It appears from press reports to be a repetition of claims previously presented extensively to the press and elsewhere and which are baseless," the Saad spokesman said.

Robin Amlot, managing editor of Dubai's Banker Middle East magazine, told Al Jazeera: "What's happening right now is causing a great deal of uncertainty.

"Banks in the UAE have been blocked by the central bank [in Abu Dhabi] from lending any more money to either of these two companies. A lot of banks around the world will be looking twice at whether they want to be lending to anybody in Saudi Arabia at all.

"So whatever the outcome of the proceedings, family enterprises, traditional Gulf family enterprises are going to have to be more transparent and more responsible in their dealings otherwise banks are not going to lend to them."