Saudi authorities are striking agreements with some of those detained in an anti-corruption crackdown, asking them to hand over assets and cash in return for their freedom, sources familiar with the matter said.

The deals involve separating cash from assets like property and shares, and looking at bank accounts to assess cash values, one of the sources told Reuters.

Dozens of princes, senior officials and businessmen, including cabinet ministers and billionaires, have been detained in the graft inquiry at least partly aimed at strengthening the power of Crown Prince Mohammed bin Salman.

These include billionaire Prince Alwaleed bin Talal, one of the kingdom's most prominent businessmen.

One businessman had tens of millions of Saudi riyals withdrawn from his account after he signed. In another case, a former senior official consented to hand over ownership of four billion riyals worth of shares, the source said.

The Saudi government earlier this week moved from freezing accounts to issuing instructions for "expropriation of unencumbered assets" or seizure of assets, said a second source familiar with the situation.

There was no immediate comment from the Saudi government on the deals and the sources declined to be identified because these agreements are not public.

Reuters could not immediately verify a Financial Times report that in some cases the government is seeking to appropriate as much as 70 percent of suspects' wealth to channel hundreds of billions of dollars into depleted state coffers.

A third source familiar with the matter said if people are willing to return "ill-gotten gains" then their punishment will be "time served" in the Ritz Carlton hotel, where they are being detained.

The Saudi authorities have help from international auditors, investigators and people with experience in tracing assets. Bank representatives are on hand to execute the decisions immediately, one of the sources said.

Saudi authorities have said they have questioned 208 people in an anti-corruption investigation and estimate at least $100 billion has been stolen through graft, an official said last week as the inquiry expanded beyond the kingdom's borders into the United Arab Emirates.

Those detained include other high-profile businessmen such as Mohammad al-Amoudi, whose wealth is estimated by Forbes at $10.4 billion, with construction, agriculture and energy companies in Sweden, Saudi Arabia and Ethiopia; and finance and healthcare magnate Saleh Kamel, whose fortune is seen at $2.3 billion.

Bankers and consultants had told Reuters that Riyadh may strike deals with detained tycoons and princes that in effect legalise their fortunes in exchange for a share of their money.