MOSCOW - Moscow observed an official day of mourning on Tuesday and nervous commuters returned to the metro, while the death toll from twin suicide bombings on the capital's underground railway rose by one to 39 people.

Flags across Moscow flew at half-mast and somber Muscovites laid flowers and lit candles at the stations hit by the blasts blamed on North Caucasus rebels.

The police presence was stepped up at Moscow metro stations, and security was tightened on the networks in cities from St. Petersburg to Novosibirsk in Siberia, local media reported.