The president, traveling back overnight from a surprise trip to Afghanistan, said the U.S. stands with Russia after female suicide bombers set off twin bombs on Moscow's subway system.

"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 in a statement. "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."

The attacks were set off during a busy morning rush hour period, and have caused 35 deaths and many more injuries so far, The New York Times reported. Russian authorities have reportedly said they believe the attacks to be an act of domestic terrorism.

"My thoughts and prayers go out to those who lost loved ones, and I wish all who sustained injuries a successful recovery," Obama added.