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Russian President Dmitry Medvedev has declared a state of emergency in seven Russian regions because of wildfires fuelled by a heatwave.

The death toll from the fires has risen to 40, the ministry of health said.

The Russian emergencies ministry said 500 new blazes had been discovered over a 24-hour period, but most had been extinguished.

91�ȱ�s have been burnt in 14 regions of Russia, the worst-hit being Nizhny Novgorod, Voronezh and Ryazan.

Nineteen of the 40 deaths recorded were in Nizhny Novgorod, the health ministry said.

The state of emergency was announced in a decree that also restricted public access to the regions affected.

Moscow is again shrouded in smoke from peat and forest fires outside the city.

The fires, caused by record temperatures and a drought, have affected cereal harvests, driving wheat prices up.

Heatwave grinds on

Prime Minister Vladimir Putin saw some of the fire damage for himself in Nizhny Novgorod region last week. On Monday, he held meetings with regional leaders in Moscow to discuss further help for affected communities.

Russians are bracing themselves for another week of high temperatures, with forecasts of up to 40C (104F) for central and southern regions.

Officials also expect stronger winds in some regions, which will fan the flames.

By Sunday night, wildfires were still raging across some 128,000 ha (316,000 acres).

Thousands of people have lost their homes and nearly a quarter of a million emergency workers have been deployed to fight the flames.

Moscow doctors say the elderly and toddlers should wear gauze masks outdoors.

The city of Kazan, on the Volga river east of Moscow, was also blanketed in smog on Monday, an eyewitness told the 91�ȱ�.

Marek Zaremba-Pike said Kazan's air "smells of burnt wood and tastes of dust".

"Usually we can see the Kazan Kremlin very clearly, but visibility is poor. You can't see it at all, just the river bank."

More famous for its bitterly cold winters, the giant country's European part normally enjoys short, warm summers.

However, July was the hottest month on record. In Moscow, which sees an average high of 23C in the summer months, recorded 37.8C last Thursday.

Emergency officials say the heat and drought are the main causes of the fires, but they also blame human carelessness, and urged people to use extreme caution when walking or driving in the woods or countryside.

"Any source of fire, including a cigarette thrown from a car window, will ignite the dried grass," the emergencies ministry said.