Shifting winds brought the acrid smell of smog briefly back to Moscow yesterday and fires burned near Russia’s main nuclear research centre as residents complained of ash in the air in central Russia.

Amid the worst heatwave in its history, Russia has for days battled to cut back hundreds of blazes across the country, including fires in a nature reserve near its top nuclear research centre in Sarov, a town still closed to foreigners as in Soviet times.

The secret nuclear research centre tucked into the woods in central Russia straddles two regions – the Nizhny Novgorod and Mordovia regions – and the emergency ministry said yesterday the number of fires in both regions had been reduced.

But the fires were still burning in the villages of Popovka and Pushta in the nature reserve where more than 1,200 people and over 150 pieces of equipment were fighting the flames, Mikhail Turkov, a spokesman for the ministry’s Volga regional branch, said.

Sergei Kiriyenko, head of Russia’s state nuclear corporation Rosatom, said he had personally inspected the area around Sarov and that there was no danger of nuclear explosions or other environmental threats even if the fire reached the territory of the centre. The threat of the fire reaching the premises of the nuclear centre, which is surrounded by forests on all sides, was “very real” several days ago but the situation is now under control, he said on Friday in comments released by Rosatom on Saturday.

“The fire is constantly spreading from the Mordovia reserve and as long as it has not been put out, this risk for Sarov will remain.” The threat of fire from the Mordovia natural reserve will only be fully eliminated once protracted rains have come. Until then, we’ll have to be on high alert,” Mr Kiriyenko added.