A British businessman who is being held in a Moscow detention center has fallen so severely ill that his lawyer says he could die at any moment.

Darren Keane, 43, CEO of the Storm International gambling holding, is accused of letting two of the company's casinos operate in the city even after gambling was banned in July 2009.

He was arrested by Federal Security Service agents June 22, charged with illegal business activities, and sent to a pretrial detention center, Vedomosti reported Friday, citing an unidentified city police source.

Keane has since unsuccessfully tried to have his arrest overturned by the city's Tverskoi District Court, which originally sanctioned it, his lawyer told the news site Rosbalt.ru late Thursday.

The lawyer, Viktoria Vasilyeva, said Keane's condition was alarming because, among other things, he suffers from thrombophlebitis, an acute inflammatory form of clotted veins, or thrombosis.

Vasilyeva warned that Keane "could die at any moment" and drew a parallel to the case of Hermitage Capital lawyer Sergei Magnitsky, who died in a Moscow pretrial detention center in 2009. "Nobody needs a repetition of what happened to Sergei Magnitsky, yet they would not lift my client's detention," she said.

The Magnitsky case grabbed headlines in Washington and Moscow last week after it was revealed that the U.S. State Department had imposed a visa ban on a number of Russian officials implicated in Magnitsky's death.

The decision caused an outcry in Moscow with President Dmitry Medvedev ordering the Foreign Ministry to prepare retaliatory steps.

The decision to keep Keane in detention was based on fears that he might flee the country, media reports said. "The Tverskoi court sanctioned his arrest on June 23 because he is not a Russian citizen and might go into hiding," the police source told Vedomosti.

Vasilyeva, the lawyer, complained that the court then rejected a plea to free him on bail of 6 million rubles ($200,000). "Darren Keane has long lived in Russia, he owns real estate here and has a Russian wife and a child. He is not planning to hide," she said.

She added that the charges against him are moderate and that if convicted he would face a maximum of five years in prison.

Keane arrived in Russia in 1997, according to his biography on Storm International's homepage. Three years later, he became general manager of Shangri-La, for years the city's most luxurious address for gamblers. In 2005, he was made a vice president, overseeing Storm International's five casinos and 20 slot machine halls.

He has been the company's CEO since September 2008. He also co-founded the Expat Football League in 2003, one of the longest-running sports organizations for expatriates in Moscow.

The British Embassy said it was aware of Keane's detention. "Consular staff are in contact with the British national and their next of kin and providing consular assistance," a spokeswoman said in an e-mailed statement, requesting anonymity in line with embassy policy.

Repeated calls to the press services of the Tverskoi and Moscow City Court went unanswered Friday, as were calls to Storm International. A city police spokeswoman declined to comment on the case.

The case is apparently part of a bigger investigation against illegal gambling in the city. A police official told RIA-Novosti on Friday that a national search warrant had been issued for other foreign executives of Storm International who are allegedly in hiding. The report did not specify their number nor publish any names.

Apparently the Federal Security Service, or FSB, has been suspicious about the company's activities since gambling was restricted to just four far-flung regions in mid-2009.

Back then "it was established that Storm International's management failed to close its Shangri-La casino and a gambling machine hall located in a concert hall on Pushkin Square," the police official said.

In April, FSB and police officers raided the premises of Shangri-La and uncovered "working roulette tables" Rosbalt.ru reported, quoting a security service source.

Investigators identified Keane as running the illegal gambling after wiretapping his telephone, the report said.

The report also said the April raid was part of a larger operation against illegal gambling.

The investigation uncovered dozens illegal casinos operating inside and outside the capital. In the Moscow region it led to a turf war among law enforcement agencies when the Investigative Committee accused regional prosecutors of protecting a network of illegal gambling halls in exchange for perks.

Several prosecutors were arrested, and at one point investigators accused Artyom Chaika, son of Prosecutor General Yury Chaika, of being a middleman between the prosecution and the gambling network.

British-born entrepreneur Michael Boettcher, who founded his first casino in Moscow in 1992, built Storm International to become a leading player in the country's once-thriving gambling industry.

When the restrictions were enacted in 2009, the company said it would move its business abroad. Subsequently, casinos were opened in Mexico, Germany and Kyrgyzstan. Storm International also operates new Shangri-Las in the capitals of Belarus and Armenia.

In Moscow, the company still operates the Radio City Bar in the Pekin Hotel.

In a possible sign of how seriously Storm International is taking the arrest, it took down its web site at storminternational.com over the weekend. A cached version could still be accessed by search engines.

Yana Yakovleva, founder of the Business Solidarity lobby group, who advocates amnesty for jailed entrepreneurs, said Keane's case seemed a little ambiguous but his nationality seemed to give him the biggest disadvantage.

 "If he were a Russian citizen, he probably would have been granted bail," she told The Moscow Times on Sunday.

Yakovleva, who founded her group after spending seven months in a pretrial detention center on charges related to her business that were later dropped, noted that the suspected mastermind of the Moscow region gambling ring has been freed.

 National media reported this spring that Ivan Nazarov, who was detained in connection with the crackdown on illegal casinos in February, was freed after entering a plea bargain with investigators.

 Even a recent bill championed by Medvedev that promises parole to thousands of entrepreneurs jailed for minor economic crimes would not help Keane, Yakovleva said.

 Medvedev has been campaigning to improve the business climate and prevent unfair prosecution of entrepreneurs by law enforcement agencies, but his initiatives largely have been ignored by officials on the ground. The bill, proposed in May, has yet to be heard by the State Duma.