The U.S. State Department said Thursday it wanted information on Umarov, the leader of the Caucasus Emirate movement. Umarov claimed responsibility for the 2010 bombing of a Moscow subway station that killed 40 people.
Russia's predominantly Muslim North Caucasus republics Chechnya, Dagestan and Ingushetia have seen an upsurge of violence recently. Russia has been fighting the insurgency for many years following two bloody conflicts in Chechnya in the 1990s.
The State Department accused Umarov's group of launching terrorist attacks in the region and issuing statements encouraging violence against its stated enemies, which includes the United States, Russia, the United Kingdom and Israel. He was listed as a specially designated terrorist by the State Department in 2010.
Leaders of the Chechen republic suggested Umarov was among those killed in an April raid. However, a man who said he was Umarov later said in a phone call to Radio Free Europe/Radio Liberty that he was alive and well.
"There was an operation in which several mujahedin died," the man said. "My death was announced, too. They won't receive any respite from me. I'm preparing my answer to them. They should expect news from me soon."
Notable deaths of 2014 [PHOTOS]