PEREDELTSY, Russia — Moscow was engulfed today by the thickest blanket of smog yet this summer, an acrid, choking haze from wildfires that have wiped out Russian forests, villages and a military base.

Passengers on Moscow's subway said the eye-stinging haze hovered above the platforms, and City Hall warned of health risks from the smoke, which is carrying harmful gases including carbon monoxide.

"I woke up before dawn and thought I was going to die of suffocation," said Yadviga Pashkova, a frail, 62-year-old former schoolteacher who lives in central Moscow. "It felt awful because there was no way out."

To the east, firefighters focused on beating flames back from a top-secret nuclear research facility. In the capital, President Dmitry Medvedev fired several high-ranking military officials over what he called criminal negligence in fires that ravaged a military base.

Russia is suffering through its worst heat wave on record, a condition that has sparked forest and peat fires across its central and western regions that have killed at least 48 people in the past week.