CIA Director William Burns on Wednesday estimated that 15,000 Russians have died in Ukraine and some 45,000 have been wounded.

Burns, speaking at the Aspen Security Forum in an interview with NBC News chief Washington correspondent Andrea Mitchell, said intelligence estimates of battlefield casualties are “always a range.”

“There’s no perfect number,” Burns said.

“I think the latest estimates from the U.S. intelligence community would be something in the vicinity of 15,000 killed and maybe three times that wounded, so a quite significant set of losses,” he continued. “And the Ukrainians have suffered as well, probably a little less than that. But significant casualties.”

Ukraine has claimed even higher numbers of Russian casualties, estimating in April that its military had killed more than 20,000 Russian soldiers.

The United Nations Office of the High Commissioner for Human Rights estimated last week that Russia’s invasion had resulted in 5,024 civilian deaths and 6,520 civilians injured.

Burns also weighed in on speculation about Russian President Vladimir Putin’s mental and physical health, saying that while he was “unstable,” the Russian leader has his “own way of looking at reality.”

“There are lots of rumors about President Putin’s health, and, as far as we can tell, he’s entirely too healthy,” Burns said. “It’s not a formal intelligence judgment.