MOSCOW - Two California women who were hospitalized in Moscow for possible thallium poisoning were flying home to the United States Wednesday, as colleagues and relatives struggled to understand how and why someone would give the two the potentially fatal chemical.

A U.S. Embassy spokesman identified the women as Marina Kovalevsky and her daughter, Yana, but gave no further details. Russian authorities were investigating when and how the women were exposed to the poison, the spokesman said, speaking on condition of anonymity because of embassy rules.

Moscow police declined to comment, but the Ekho Moskvy radio reported police were investigating cafes and restaurants in the area of the hotel where the women had been staying.

The hospital where they have been treated since falling ill on Feb. 24 said Wednesday morning that they were in moderately serious condition and Moscow's top public health doctor, Nikolai Filatov, was quoted by the RIA-Novosti news agency as saying that thallium poisoning had been confirmed.

The two were scheduled to arrive back in Los Angeles Wednesday afternoon on an Aeroflot flight from Moscow.

Both Marina, 49, and Yana, 26, are Soviet-born and emigrated to the United States in 1989, and have visited Russia repeatedly since then, relatives and colleagues said.

In West Hollywood, Calif., where Marina Kovalevsky opened an internal medicine practice some six or seven years ago, relatives said she left for Moscow on Feb. 14 to attend a friend's party.

Surrounded by the cities of Los Angeles and Beverly Hills, West Hollywood has a large Russian-speaking immigrant community.

Oyuna Chuluun, a medical assistant at Kovalevsky's storefront clinic, said she thought the apparent poisoning an accident. She said Marina was divorced.

"We just don't believe someone would want to poison her," Chuluun said.

A colleague, Dr. Arkady Stern, told The Associated Press that Marina Kovalevsky left Los Angeles "in a good state of health, in good spirits."

Stern said that after it was suspected that she was poisoned, she was given dialysis and took an antidote called "Prussian Blue" and her condition began to improve. He said that since both had the same symptoms, it led to the suspicion that they were poisoned but he believed it was "some sort of tragic mistake."

There was no indication of whether the women had business or political interests in Russia that could have made them a target for poisoning.

"She (Marina) didn't have enemies. Everybody loved her. She's a great doctor," Stern said.

Olga Tabarovskaya, a cousin of Marina Kovalevsky and a chiropractor, said she spoke with the elder Kovalevsky two nights ago.

"She said she was tired but was very anxious to come back," Tabarovskaya said.

How the two may have ingested the poison - a colorless, tasteless substance that can be fatal in doses of as little as one gram - was not clear.

Thallium is a reputed poison of choice for assassins. It was initially suspected to be the toxin used in last year's fatal poisoning in London of former Russian security agent Alexander Litvinenko, but it was later determined he had 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.

In the past, thallium has been used in rat poison and it continues to be used industrially to manufacture products including glass lenses, semiconductors, dyes and pigments.

Thallium was used by Saddam Hussein, who poisoned several of his Iraqi opponents. It also reportedly was considered by the CIA for use against Fidel Castro, possibly by putting thallium powder in his shoes to prompt loss of his trademark beard.

Associated Press Writer Alicia Chang and APTN correspondent Steve Fluty contributed to this report from West Hollywood.