Polish firefighters work to extinguish flames and prevent new fire outbursts outside the village of Ryabinovka, some 180 kilometres southeast of Moscow on Aug. 15. (Mikhail Voskresensky/Reuters)

The number of wildfires in Russia has shrunk significantly, but clouds of acrid smog generated by them still hung over the Russian capital Wednesday.

An environmental watchdog in Moscow said that the level of carbon monoxide, hydrocarbons and other pollutants in the air continued to exceed safe limits Wednesday.

Smoke has periodically shrouded large sections of the city since the weekend, but pollution remained below its peak levels from earlier this month when smog choked Moscow for a week.

The Emergency Situations Ministry said the area covered by wildfires around Moscow has been halved since Tuesday, but four forest and five peat bog fires were still burning.

The ministry said that the amount of land on fire countrywide has been reduced by about 10 per cent to about 20,000 hectares, which is about a 10th of the territory they covered earlier this month when wildfires were at their peak.

Also Wednesday, Moscow regional police said four suspected arsonists were detained in a town some 70 kilometres southwest of Moscow, the Interfax news agency reported.

Police in the town of Naro-Fominsk told Interfax that one of the men tried to set fire to a forest near a gas station. The other three attempted to burn down a disputed storage facility where large quantities of food and beer were kept.

The hottest summer since records began 130 years ago has sparked thousands of fires in Russia. More than 50 people have died directly in the wildfires across Russia, and more than 2,000 homes have been destroyed.

Drought has cost Russia a third of its wheat crop, prompting the government to ban wheat exports through the end of the year.