The number of foreign workers sickened by food poisoning at the construction of a new terminal at Moscow's Sheremetyevo airport has risen to 433, a food safety watchdog spokesperson said Monday.

The mass food poisoning hit the Turkish construction company Enka's summer camp near Moscow last week. Local food safety officials said earlier that all patients, mainly nationals of Georgia, Uzbekistan and other former Soviet states, had been diagnosed with salmonella infection.

"Three hundred and seventeen people are in hospital in [nearby] Solnechnogorsk, and another 116 are being treated at the Morozovka holiday center, where they have been accommodated," Olga Gavrilenko said.

Gavrilenko said all the patients were receiving appropriate treatment and food, and that none of them had been released from hospital yet.

The first cases of salmonella - a potentially lethal infection that affects the gastrointestinal system - were reported Tuesday evening. The food safety and consumer rights watchdog said that drinking water was not to blame, adding that food might have been the source of the poisoning.

The Prosecutor's Office of the Moscow Region said that an investigation into violations of sanitary norms had been launched, and that charges envisioning up to three years in prison might be brought against those found responsible.

Workers from former Soviet republics are the main source of cheap labor for numerous construction projects in booming Moscow and its environs, many of which are implemented by Turkish firms.

The poor working and living conditions of migrant workers, who are often in Russia illegally, have been repeatedly criticized by the governments of former Soviet republics and rights groups.

Over 300 foreign and Russian construction workers suffered from food poisoning in Moscow and nearby districts last summer.