Former Russian spy Alexander Litvinenko was fighting for his life yesterday after his condition worsened further, doctors and friends said, as mystery deepened over what caused his condition.
Friends also reported that Litvinenko had suffered a heart attack in the London hospital where he is in intensive care.
In their latest update doctors ruled out an initial theory that the heavy metal thallium was responsible, said radioactivity was "unlikely" and dismissed a report of three unidentified objects had been found in his intestines.
Litvinenko fell ill with poisoning three weeks ago shortly after meeting two Russian contacts, sparking accusations that the Kremlin was behind a Soviet-style sting against him.
In another development on that front, the Times reported that detectives had identified a Russian known only as "Vladimir" whom Litvinenko had told them made him suspicious.
But the immediate focus is on his health.
"We can confirm that there was a dramatic deterioration in Alexander Litvinenko's condition overnight and he is critically ill in intensive care," said Geoff Bellingan, from University College Hospital London.
"He can also be more effectively isolated to protect him against infection, following the damage to his immune system," the hospital said.
But they scotched a BBC report earlier yesterday that small, round objects of "dense matter" -- possibly packages -- were discovered when doctors took X-rays of Litvinenko's stomach on Wednesday.
One of the objects was in his left abdomen, another in his colon and a third in his small bowel while one may have ruptured, said the broadcaster quoting unnamed sources.
The report said it was not clear whether they were connected to his condition.
Bellingan, the hospital's clinical director of critical care, called the report "misleading." The three shadows were from Prussian Blue, a non-toxic therapeutic agent used in his treatment.
"We are now convinced that the cause of Mr Litvinenko's condition was not a heavy metal such as thallium. Radiation poisoning is also unlikely. Despite extensive tests, we are still unclear as to the cause of his condition," he said.