A Russian opposition leader critical of President Vladimir Putin said he narrowly escaped death after being poisoned with a substance his doctors still have not been able to identify.
Vladimir Kara-Murza claimed his survival shows there are "near misses" in the Russian government's campaign to silence its political opponents.
He said the official diagnosis was toxic action by an undefined substance. He suffered multiple organ failure and was placed in a medically-induced coma for several days.
Kara-Murza was testifying on Wednesday before a Senate sub-committee on Capitol Hill, Washington. He is vice chairman of Open Russia, a private foundation run by exiled Kremlin critic Mikhail Khodorkovsky.
The incident in early February was similar to a mysterious poisoning he suffered two years earlier, when he nearly died from kidney failure. Both episodes were in Moscow.