A Russian medical source and police tell CBS News that two American citizens have been released from a Moscow hospital, where they were being treated for poisoning, according to the U.S. Embassy.
A Russian health official said the Soviet-born mother and daughter were being treated for thallium poisoning.
An embassy spokesman identified the women as Marina Kovalevsky and her daughter Yana, but gave no further details. Russian daily The Moscow Times reported that the women are from the Los Angeles area.
The medical source told CBS News that both women left the hospital in "satisfactory" condition.
The sources said they left on a flight for the United States at 6 a.m. Eastern time. Their exact destination was not immediately known.
The women have been treated since falling ill on Feb. 24. Moscow's top public health doctor, Nikolai Filatov, was quoted by the RIA-Novosti news agency as saying that thallium poisoning had been confirmed.
Sources told CBS News there is no threat to their lives.
Russian news reports said both women are Soviet-born and emigrated to the United States in 1989, and that they have visited Russia repeatedly since then. The reports say they arrived in Moscow in mid-February to attend a wedding.
How they may have ingested the poison — a colorless, tasteless substance that can be fatal in doses of as little as one gram — was not clear.
The New York Times reported Wednesday that Marina Kovalevsky is a physician in California, and that another doctor filling in for her during her vacation says she was healthy when she left the U.S.
Russian authorities are investigating when and how the women were exposed to the poison, the spokesman said, declining to be named because of embassy rules that prevent him from being identified.
Moscow police had no comment, but the Ekho Moskvy radio said police were investigating cafes and restaurants in the area of the hotel where the women had been staying.
There was no indication of whether the women had business or political interests in Russia that could have made them a target for poisoning.
Detectives are also not ruling out that they women may have been poisoned before they came to Russia, CBS News reports.
Thallium has the reputation as a poison of choice for assassins.
It was initially suspected in last year's fatal poisoning in London of former Russian security agent Alexander Litvinenko, who was later determined to have ingested the rare radioactive isotope polonium-210.
For poisoning purposes, thallium would be in a powdery or crystallized state. The poison works by knocking out the body's supply of potassium, essential for healthy cells, and attacking the nervous system, the stomach and kidneys. Its effects are not immediately noticeable and frequently take weeks to kick in; symptoms include hair loss and a burning sensation in extremities.
Thallium has been used in rat poison in the past, and it is still used to make lenses, semiconductors, dyes and pigments.
Thallium was used by Saddam Hussein, who poisoned several of his Iraqi opponents. The CIA also reportedly considered using thallium against Fidel Castro.