New Delhi - Indian Prime Minister Manmohan Singh on Sunday expressed deep shock and sorrow over the bomb attack in Islamabad in a letter to his Pakistan counterpart Yousef Raza Gilani.

Singh said India strongly condemned the act of terrorism and said the attacks were a grim reminder of the challenges posed by "destructive forces" which had pitted themselves against the values of democracy, pluralism and the voices of moderation.

"The prime minister further stated that such forces threaten peace and stability of each of us individually and all of us collectively and that they should not be allowed to succeed," an Indian Foreign Ministry release said.

The bomb attack in Pakistan capital Islamabad came just a week after a series of bombs went off in busy markets in Indian capital Delhi. (dpa)