Two US women hospitalized for suspected thallium poisoning were in fair condition on Thursday as authorities tried to determine why they fell ill while vacationing in Russia.
"It is still too early to determine exactly what may have caused their illness," Cedars-Sinai Medical Center said.
Marina Kovalevsky, 49, and her daughter, Yana, 26, were being treated for "presumptive" thallium poisoning and no date had been set for their release, the statement said.
The women declined to talk about their ordeal after they arrived at Los Angeles International Airport on Wednesday from Moscow. They were taken in wheelchairs past news media into waiting ambulances.
"I don't feel well, I'm going straight to the hospital, no comment," Yana Kovalevsky told reporters at the airport.
The women had been treated at a Moscow hospital after they fell sick on Feb. 24. A US Embassy spokesman there said Russian officials were investigating how and when they could have come into contact with the poison.
Moscow police declined to comment, but the Ekho Moskvy radio reported authorities were checking cafes and restaurants in the area of the hotel where they stayed.
The Kovalevskys are Soviet-born and emigrated to the US in 1989. Relatives said the two left for Moscow on Feb. 14 to attend a friend's party.
Marina Kovalevsky was "in a good state of health, in good spirits" when she left, colleague Arkady Stern said.
After it was suspected she was poisoned, Marina Kovalevsky was given dialysis and took an antidote and her condition began to improve, Stern said.
Although both women had the same symptoms, he believed it was "some sort of tragic mistake."
How the two might have ingested the poison -- a colorless, tasteless substance that can be fatal in doses of as little as 1g -- was not clear.
Thallium is the reputed poison of choice for assassins. The poison was initially suspected to be the toxin used in last year's fatal poisoning in London of former Russian spy Alexander Litvinenko, but it was later determined he had ingested the rare radioactive isotope polonium-210.
Hospital officials in Los Angeles said it did not appear the mother and daughter had ingested anything radioactive.
There was no indication 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.