'Central Chinese government officials firmly believe that Sands has permitted CIA/FBI agents to operate from within its facilities,' said report

Billionaire gambling magnate Sheldon Adelson, pictured in 2008, is thought to have given the Republicans $93m in 2012

China feared the CIA was using Macau casinos owned by Republican fundraiser Sheldon Adelson to entrap Beijing officials, according to a report commissioned by his company.

The 'highly confidential' document says Beijing believed several US-owned establishments were working in league with American intelligence.

It states that Sands Macau, owned by billionaire gambling magnate Adelson, was 'the primary subject' of claims by Chinese officials of collusion with the CIA.

Adelson is thought to have spent $93million on the Republican's 2012 election campaign.

The report said: 'Many of the (Chinese) officials we contacted were of the view that US intelligence agencies are very active in Macao and that they have penetrated and utilized the US casinos to support their operations.;

The investigation was commissioned by the Macau branch of Adelson's company, Sands China, amid concerns that the former Portuguese colony's government was working against Sands and the gambling industry in general.

The report, published in the Guardian, does not say Sands was complicit in US intelligence activity - only that Chinese officials believed this was the case.

A croupier poses at the opening of the Sands Casino in Macau in 2005. The Chinese government has become concerned by the amount of money gambled away by its own officials on trips to the city

'A reliable source has reported that central Chinese government officials firmly believe that Sands has permitted CIA/FBI agents to operate from within its facilities. These agents apparently "monitor mainland government officials" who gamble in the casinos,' the report said.

The investigation has only come to light due to a wrongful dismissal lawsuit being filed by the former head of Sands's Macau casinos.

Steven Jacobs, who is suing the company and 81-year-old Adelson has alleged in court documents that Adelson demanded he use 'improper leverage' against senior government officials in Macau to promote the company’s business interests.

He also alleges that the billionaire casino magnate demanded he commission 'secret investigations of high ranking Macau officials'.

Adelson, in court testimony earlier this year, strongly denied any improper conduct in the running of his casinos.

The 2010 report, marked with a warning not to be released in mainland China, was among a collection of Sands documents filed with the Las Vegas court hearing the case.

Sands commissioned the report at a time when Adelson, according to his own court testimony, was worried about the restrictions being placed on the growth of the gambling industry in Macau.

His company has since described the report as 'a collection of meaningless speculation'.

Beijing believed a number of US-owned establishments, including Adelson's Sands Macau (pictured) were being used by foreign intelligence agents to entrap and blackmail Chinese officials

Ron Reese, the company's senior vice-president for global communications and corporate affairs, said: 'As for the document's narrative that Sands is a front for US intelligence efforts, well that sounds like an idea for a movie script.'

Macau's gambling scene has long been a source of global intrigue - with its stream of wealthy players, high-rollers and rumoured ties to organised crime.

The newly revealed report is not the first to identify rumors of spies and international intelligence agencies seeking to exploit high-ranking officials gambling in the enclave's casinos.

In recent years, the Chinese government has become concerned by the amount of money gambled away by its own officials on trips to Macau.

The report states that an internal Central Government agency estimates around $2billion is gambled away every year by visiting Chinese government officials.

Last year, a government crackdown on corruption in Macau featured a strict enforcement of a pre-existing ban on travel to the gambling haven by public officials and wealthy punters.

The report suggests it wasn't just corruption Beijing feared, but exploitation from foreign intelligence agencies of those who lost in the casinos and ran up debts.

Beijing believed the US were eager to exert influence in Macau and even refused to allow them to open a a consulate in the territory.

Macau is one of the world's richest cities and is thought to be the most densely populated region in the world. It is one of the two provincial-level special administrative regions of China, the other being Hong Kong.