DUBAI/ZURICH: Saudi Arabia has announced it will confiscate money and assets held by dozens of top officials and businessmen detained in an anti-corruption crackdown.

But the experiences of two other Arab states trying to recover stolen money, Egypt and Tunisia, suggest Riyadh may face years of legal and diplomatic battles to secure assets held abroad. Even then success is not guaranteed.

The anti-corruption committee that detained princes, tycoons and ministers at the weekend has the power under a royal decree to take "whatever measures are deemed necessary" to seize companies, funds and other assets without waiting for the results of criminal investigations.

The offshore scrutiny of assets has already begun in the Gulf region, where Saudi Arabia regularly shares information.

The United Arab Emirates' central bank and securities regulator has asked banks and finance companies there to provide information on the accounts of 19 Saudi citizens, banking sources told Reuters on Thursday.

The Saudi committee has not given details of the allegations individuals face, though Saudi officials say they include money laundering, bribery, extortion and taking advantage of public office for personal gain.

Riyadh has also set no timetable for its confiscations, although banking sources say more than 1,700 domestic bank accounts have already been frozen at the request of the central bank.

If the committee were to try to retrieve all the revenue that has been lost to corruption, from bribes to illegal expropriation of land, the total would be $800 billion, an official at the Riyadh Chamber of Commerce and Industry has estimated.

A large amount of the funds are believed by financial sources to be held offshore in bank accounts, portfolio investments, corporate shareholdings and real estate. Many of the businessmen detained have private planes -- one has a Boeing 747 airliner.

And a study by the US National Bureau of Economic Research estimated Saudis have stashed away wealth equivalent to over 55 percent of the country's gross domestic product in foreign tax havens -- an amount exceeding $300 billion.

But Egypt and Tunisia's experiences show that although asset freezes can be arranged within months, repatriating the money can take many years.

Cairo has tried unsuccessfully for five years to retrieve about 85 million pounds ($111 million)in British bank accounts belonging to the inner circle of former President Hosni Mubarak.

British officials have said they are bound by British law, which requires the Egyptians to provide them with criminal convictions first.

Tunisia has so far recovered only a small portion of about $35 million claimed from Switzerland following the 2011 revolution that inspired the Arab Spring uprising.

DETAILED EVIDENCE

There are some precedents that could give Saudi Arabia cause for hope that it will be able to repatriate money.

Last year, Nigeria and Switzerland signed a deal paving the way for the return of over $300 million confiscated from the family of Nigeria's former military ruler Sani Abacha.

Requests from Egypt, Tunisia, Libya and Syria have led to nearly 1 billion Swiss francs ($1 billion) of assets being frozen by Swiss authorities.

But the efforts of Egypt and Tunisia to retrieve the money have stumbled over a requirement to submit evidence that would be admissable in Western legal systems, proving the beneficial owners of the assets and showing that corruption has taken place. Often assets are held in complex offshore vehicles making it hard to show who really owns them.

Carlo Lombardini, a banking lawyer and professor of banking law at University of Lausanne, said Riyadh would have to provide detailed evidence proving how the money was obtained to seize assets in Switzerland on the grounds of corruption.

"And then there is an issue whether this person in Saudi Arabia can defend themselves, and whether they benefit from a proper defence," he said.

Saudi officials would have to satisfy Swiss authorities that owners of assets had been given due process. This could be difficult given the speed and the scale of the crackdown, and the sweeping powers given to the anti-corruption committee.

The Saudi attorney-general said on Monday that detailed questioning of detainees had already produced "a great deal of evidence", but gave no more details. Senior Saudi officials did not respond to requests for information on the investigation.

A Gulf-based lawyer familiar with international corruption cases said there were two channels through which Saudi Arabia could pursue assets abroad.

In cases where Riyadh had a signed a treaty or convention with a foreign country, it could use this to obtain assistance gathering evidence before seeking to seize assets via the court system. However, Saudi Arabia does not have such a treaty with the United States, Switzerland and many other countries.

Saudi Arabia could also send a letter of request to a relevant ministry in the other nation. This would be a test of its diplomatic influence in foreign capitals.

Businessmen in detention include international investor Prince Prince Alwaleed bin Talal, whose wealth was estimated by Forbes magazine before the crackdown at $17 billion; Mohammad al-Amoudi at $10.4 billion, with construction, agriculture and energy companies in Sweden, Saudi Arabia and Ethiopia; and finance and healthcare magnate Saleh Kamel at $2.3 billion.

Repatriating assets could be so hard that Riyadh may try to avoid foreign legal action altogether in many cases, instead making deals with detained tycoons and princes that in effect legalise their fortunes in exchange for a share of their money, some bankers and consultants say.

"The government will also strike deals with businessmen and royals to avoid arrest, but only as part of a greater commitment to the local economy," said Ayham Kamel, Eurasia Group's practice head, Middle East & North Africa in a note.