He said it was a "tragic reminder" that the evil of terrorism that still threatened the US and India and "lurks in our cities".
"The people of India join me in condemning the attack in the strongest terms. We stand in solidarity and sympathy with the bereaved families, the injured and the people of the United States," he said expressing shock and sadness over the attack.
Singh also offered full support to the US in the investigations into the attack.
At least two persons were killed and 23 others injured in two blasts near the finish line of the annual Boston marathon yesterday.