Russian authorities say two American citizens are being treated in a Moscow hospital for poisoning by the deadly chemical substance thallium.
Officials of Russia's consumer protection agency, Rospotrebnadzor, say the two women, aged 42 and 26, are being treated in the Sklifosovsky Institute.
Russian media reports identify the two as Marina Kovalensky and her daughter Yana. Officials say they were admitted to the clinic last week. Their condition is described as fairly serious.
The two women were staying at a Moscow hotel when they became ill. It took several days to establish they were poisoned with thallium.
Officials at the U.S. Embassy in Moscow say they are in close contact with the victims' families and are assisting them.
Thallium is a colorless and odorless poison.
It was initially suspected as the agent in last year's poisoning death in London of former Russian intelligence agent Alexander Litvinenko. But investigators later determined he had ingested the rare radioactive isotope polonium 210.
Some information for this report was provided by AFP and AP.