Moscow (CNN) -- Explosions that rocked two subway stations in central Moscow during Monday morning rush hour are being investigated as acts of terrorism, authorities said.
Suicide bombers were suspected, the Russian prosecutor's office said.
The blasts killed at least 35 people and wounded 40 others, Russia's Emergency Situations Ministry said. The casualty tolls were fluctuating immediately after the blasts.
The first explosion occurred about 8 a.m. at Lubyanka subway station, killing at 23 people and injuring 20.
The Lubyanka station is near the Kremlin and the nation's intelligence service, the Federal Security Service.
Another blast happened about 30 minutes later at Park Kultury station, on the same train line. The Emergency Situations Ministry reported 12 dead in the second explosion, with 20 more injured.
Millions of commuters use the Moscow metro system every day.
A Web site associated with Chechen separatists claimed responsibility for the attacks.
Immediately after the explosions, officials had cast suspicion on the separatists.
Chechens have long fought for independence from Russia.
Chechnya is a southwestern Russian republic, in the Caucasus Mountains region. Chechnya's population of 600,000 to 800,000 is primarily made up of Sunni Muslims and Russian Orthodox Christians. Thousands have been killed and 500,000 Chechen people have been displaced in their conflict with Moscow.
A Chechen female suicide bomber in August 2004 killed nine people and herself, and wounded 51 others, when she detonated a bomb outside a subway station in northeastern Moscow. In February 2004, a suicide bomber detonated a bomb on a Moscow metro train, killing 40 people and injuring 100 others. A suicide attack in 2003 killed 15 people at a Moscow concert.
Chechen terrorists killed hundreds in 2004 at a school in Beslan, Russia. They also were suspected in the downing of two Russian airplanes that year in an attack that killed 89.