Yushchenko aide 'warned of danger'
Recovering from dioxin poisoning, Yushchenko looks ahead to elections.
CNN's Dr. Sanjay Gupta says dioxin causes damage to internal organs and could cause cancer in the long term
Doctors say dioxin is responsible for the illness that has afflicted Yushchenko.
(CNN) -- The chief of staff to Ukrainian opposition leader Viktor Yushchenko says he was warned more than four months ago that the politician's life could be in danger.
Former Secret Service police officers told him in late July "that they would try to get rid of or 'take care' of Yushchenko, and that the primary way would be poison," Oleh Rybachuk told CNN.
In response to the threat, the candidate's security was beefed up, "but obviously, not enough," he said.
Rybachuk's comments came hours after Yushchenko returned Monday to Kiev after being discharged from a hospital in Vienna, Austria, where his doctors said tests showed he had been poisoned with dioxin.
Yushchenko accused Ukrainian authorities of being behind the apparent attempt on his life. "Investigation will take some time," he said.
He noted Ukraine's prosecutor-general has reopened a probe into his illness.
"If (the) general prosecution of Ukraine will act according to the law, as I hope, Ukraine and the whole world will know who was in charge of it."
Ukraine lawmakers also have reopened their own investigation.
"The results of the most recent expertise in Vienna are giving us grounds to renew our work," The Associated Press quoted lawmaker Volodymyr Sivkovych as saying.
"However, we are not convinced that deliberate poisoning can be proved."
Sivkovych, who supported Yushchenko's presidential opponent, Prime Minister Viktor Yanukovych, will lead the parliamentary commission looking into Yushchenko's ailment.
Sivkovych led an earlier commission that investigated the case in October. That panel decided Yushchenko had suffered a combination of a viral infection and several other diseases, AP reported.
In Washington, White House Press Secretary Scott McClellan reacted Monday to the report that Yushchenko had been poisoned.
"It's terrible news to hear and certainly disturbing reports," he told reporters. "I know the Ukraine government is investigating this matter fully, as they should."
McClellan also denied allegation made earlier in the day by Yanukovych that Washington was financing his opponent's campaign.
In an interview with AP, Yanukovych said, "The United States' meddling into Ukraine's internal affairs is obvious. It is demonstrated by the financing of Yushchenko's campaign."
Asked whether the U.S. government has funded the Ukraine opposition, McClellan said, "We do not and have not supported any particular candidate in Ukraine's election."
But the U.S. government has given money to "support free and fair elections around the world," including to non-governmental and other international organizations in the Ukraine, he said.
The funds -- for voter education and political party training -- have been "made available to all political parties in Ukraine," he said.
The Bush administration has spent more than $65 million the past two years to aid political organizations in Ukraine, but none went to political parties, AP reported U.S. officials as saying.
Meanwhile, one of the doctors who oversaw Yushchenko's treatment in Vienna said the diagnosis of dioxin poisoning was "rock solid" but added that more information must be obtained before medical authorities can determine his prognosis.
Dr. Michael Zimpfer told CNN he based his conclusion on a physical examination of the patient and "various blood tests" carried out at Vienna's Rudolfinerhaus clinic and elsewhere.
Zimpfer told reporters over the weekend that the concentration of dioxin in Yushchenko was "1,000 times above the normal levels" and that he suspected "third-party involvement."
Yushchenko, 50, has previously accused Ukrainian authorities of having tried to poison him in the run-up to November's fraudulent presidential election.
Ukraine's Supreme Court voided the election's outcome after Yushchenko lost to Prime Minister Viktor Yanukovich, and a rerun of the contest is set for December 26.
Yanukovich has denied any role in the poisoning.
Yushchenko, then a telegenic campaigner, was taken to the Vienna hospital in September after he first fell ill. He resumed campaigning later in the month, his face pockmarked and disfigured.
"I have heard a lot of stories and legends on how this poison has been delivered, where it has been produced, which secret services were used for delivering it in Ukraine," Yushchenko said Monday.
"I am not eager to comment on all this stuff, because it's a very delicate point. I do not want to put any shade on somebody, before it was established by the court."
Though Yushchenko's face gave the most startling evidence of poisoning, an expert on dioxin said the candidate could suffer other, more serious threats.
Given what little medical information has been released publicly, Yushchenko could have been exposed to any of about 20 dioxins or dioxin-like chemicals, said Dr. Arnold Schecter, professor of medicine at the University Texas School of Public Health at Southwestern Medical Center in Dallas.
"Some persist for decades ... some of the others start leaving the body very rapidly and will be completely gone in a few years, not a few decades."
Absent a detailed analysis by an accredited laboratory, "I don't know if they're talking about one or all the dioxins," he said.
But Zimpfer, citing privacy concerns and sensitivity by some government agencies that they could be perceived to be taking sides in the political debate, would not divulge the names of the laboratories that carried out the tests or the details of their findings.
Dioxin exposure can cause a host of ills, including irritability, insomnia, headaches, cramps, lethargy, cancer, underactive thyroid and diabetes, said Schecter, who has written a reference book on dioxins and health used by medical professionals.
"You absolutely need to know what laboratory did the analysis and what those results were," he said. "Which dioxins were there?"
"That's absolutely correct," agreed Zimpfer, who trained as an anesthesiologist and is director of the Rudolfinerhaus clinic, where Yushchenko was treated and discharged Sunday.
"With regard to the distribution and elimination from the body, the kinetics of the poison in the body and also the final prognosis, we still are lagging behind."
Yushchenko suffered not only liver damage but also damage to his gastrointestinal tract, small and large bowel, stomach and pancreas, Zimpfer said.
Still, Zimpfer said Yushchenko is in good spirits and feels good, though he remains on pain medication, is taking topical medication for his facial lesions and a medication intended to block the reuptake of dioxin by the liver.
"He's in perfect strength, planning to go skiing in the near future and, in case he gets elected, he certainly has the strength and the mental vigor to run (the country)," said Zimpfer, who added that he supports neither side in the political contest.
A reliable prognosis could be critical for voters who must decide this month whether to make Yushchenko their president.
While only rarely used as a poison, dioxin can be easily obtained from any chemical supply house or can be synthesized in a fairly simple procedure by a chemist, Schecter said. "One drop will do it."
The development is political dynamite in what has been a turbulent political few weeks in Ukraine. The election process has drawn international attention with the West-leaning Yushchenko vying with the Russian-backed Yanukovich, in what has been seen as almost a proxy cold-war dispute.