"It is with great anguish that I have learnt of the bomb blasts in Moscow, which have led to the loss of so many innocent lives. This is most tragic and horrific act of violence," Singh said in a letter to the Russian leader.
It further said "at this difficult hour, our thought are with you, the people of Russia and the families and friends of the victims of this terrible tragedy. On behalf of the government and people of India, I convey our deepest condolences.
"I wish to assure you that India stands united with Russia in combating the forces of violence and terrorism."
Condoling the loss of lives in the twin suicide attacks, External Affairs Minister S M Krishna said "India condemns these horrendous attacks and my sympathies go out to those who have been killed and who have suffered in this attack."
Two suicide bombers attacked Moscow’s busy subway system during the morning rush hour killing at least 37 people and injuring over 30 others near the Kremlin and the Federal Security Service headquarters.
In a statement, the External Affairs Ministry said the government strongly condemns the bomb blasts and reiterated its conviction that only collective efforts by the international community can combat the scourge of terrorism that the world is facing today.
The Government hopes that the perpetrators of these senseless attacks will be brought to justice, it said.