U.S. Defense Secretary Jim Mattis said on July 14 that the United States cannot prove that Islamic State leader Abu Bakr al-Baghdadi is dead.
Earlier this week, the Syrian Observatory for Human Rights said it had "confirmed information" that Baghdadi was killed. And Russia's army said last month that it was seeking to verify that it had killed the IS chief in a May air strike in Syria.
But U.S. and Iraqi officials have been skeptical.
"If we knew, we would tell you. Right now, I can't confirm or deny it," Mattis said. "Our approach is we assume that he's alive until it is proven otherwise, and right now I can't prove it otherwise."
Mattis added that a cease-fire in southwestern Syria that the United States negotiated with Russia is holding so far.
The cease-fire deal was announced after U.S. President Donald Trump's first meeting with Russian President Vladimir Putin last week in Germany.