U.S. President Barack Obama on Monday condemned the twin bomb attacks in Moscow's subway system and offered his condolences to the Russian people.

"The American people stand united with the people of Russia in opposition to violent extremism and heinous terrorist attacks that demonstrate such disregard for human life, and we condemn these outrageous acts," said Obama in a written statement.

Two explosions hit the Moscow subway system Monday morning, killing at least 37 people and injuring some 102 others.

No one has claimed responsibility, but Russian security officials reportedly said terrorists from the Northern Caucasus could be behind the deadly attacks.

"I send my deepest condolences to the people of Russia after the terrible loss of life and injuries resulting from the bombings on the Moscow metro," Obama said. "My thoughts and prayers go out to those who lost loved ones, and I wish all who sustained injuries a successful recovery."