The U.S. State Department identified the women as Marina Kovalevsky and her daughter, Yana. They were hospitalized on February 24 with symptoms of poisoning.
Speaking in Washington March 6, State Department spokesman Sean McCormack said U.S. government officials are in contact with the family of the women.
"Russian authorities are now conducting an investigation to try to determine when and how this happened," McCormack said. "Our consular officers are in direct contact with the Kovalevsky family to offer whatever assistance we can while they are hospitalized in Russia as well as helping them return back to the United States."
According to Russian press reports, the two were born in the Soviet Union and emigrated in 1989. The reports say the women arrived in Moscow in mid-February to attend a wedding.
Aleksandr Litvinenko: A Timeline
CLOAK AND DAGGER: A timeline of a murder case that unraveled after Andrei Litvinenko, a former Russian security officer and vocal Kremlin critic, dies on November 23, 2006, of poisoning by radioactive isotope polonium-210.
In a deathbed letter, Litvinenko blames Russian President Vladimir Putin for his death -- a claim Putin condemns.
Investigators center on two meetings in London that Litvinenko had described -- one in which he met with two Russians for tea in London, and another in which he met with a third Russian at a sushi bar.
Six months later, British prosecutors announce they have enough evidence to charge a Russian citizen -- one of the men who had met with Litvinenko for tea -- with the murder ...more...
MORE: Coverage in Russian from RFE/RL's Russian Service.