Millions of Muscovites were advised to stay indoors as thick smog from forest fires choked the city. Schoolchildren were kept inside and officials warned that pregnant women and people with heart conditions should take extra precautions as the fires raged in peat bogs and forests around the rim of the capital. "We are concerned about children and pregnant women as they are the most sensitive to this," Russia's chief medical officer, Gennady Onishchenko, said.