Moscow remained shrouded in a blanket of smog for a second day Thursday, and officials said forecast rain showers would bring little relief as winds continued to blow in smoke from peat fires in the surrounding region.

Light rain showers are forecast from Friday through Tuesday, "but to extinguish the fires, the rain has to be very strong," said Natalya Yershova, a spokeswoman for the Federal Meteorological Service.

Even heavy rain, however, might not be enough, as rain can only help to put out forest fires, whereas a majority of the 20 fires in the Moscow region as of Thursday were peat bog fires, which smolder from within, Emergency Situations Ministry spokeswoman Oksana Brik said. "We can't ever depend on rain to do the job," Brik said.

More than 500 firefighters were working to extinguish the fires Thursday, a majority of them in the region's eastern Orekhovo-Zuyevsky district, where 10 fires were burning, she said.

Murat Nakhayev, a specialist with Moscow Ecological Monitoring, a municipal agency, said overall air quality in the city should improve slightly over the next few days with the rain and overcast skies. He advised people with respiratory problems to avoid traffic-congested streets, where exhaust fumes mix with the smoke.

Emergency Situations Minister Sergei Shoigu said the Moscow region fires were likely caused by intrepid mushroom gatherers. "I think you know that different types of mushrooms grow very well in peat bogs, ... and people head out there en masse for such activities," Shoigu told a State Duma session on Wednesday.

Vladimir Zhirinovsky, the flamboyant leader of the ultranationalist Liberal Democratic Party, suggested Wednesday in the Duma that arson, sabotage or even something from outer space had caused the fire. It was unclear whether he meant extraterrestrial or man-made space technology.