A bombing at a major Shiite Muslim mosque in Pakistan's largest city, Karachi, has left at least 15 people dead and dozens injured. The incident has prompted violent rioting in the area. The blast marks the second act of apparent religious violence there in as many days.

The explosion caused massive damage at the Imam Bargah Ali Raza mosque, a major Shiite house of worship in downtown Karachi.

Police say a bomb was planted inside the mosque and detonated during Monday evening prayers.

A witness standing in front of the building at the time of the explosion describes a blinding flash of light and scattered human remains.

The explosives used were strong enough to damage the mosques dome, high above the prayer hall, and to shatter the windows of surrounding buildings.

The incident sparked rioting in the area, with an angry crowd torching two gas stations and a police car, while chanting anti-government slogans and Shiite religious mottos.

Some rioters also expressed anger at the United States, which, though allied with Pakistan, is often seen by some religious Pakistanis as seeking to undermine the Muslim world.

The blast occurred one day after the assassination of Mufti Nizamuddin Shamzai, a well-respected cleric among Pakistan's majority Sunni Muslims.

Mr. Shamzai's killing prompted citywide rioting, which subsided following the religious leader's funeral that evening.

Pakistani Interior Secretary Abdur-Rauf Chaudry told VOA the mosque bombing is likely a response by Sunni extremists to the assassination.

"It is a chain reaction," he said. "Yesterday's killing [of Mufti Nizamuddin Shamzai] was a very high-profile killing, and we were apprehensive of the backlash, which happened more quickly than we expected."

While Pakistan's majority Sunni and minority Shiite Muslims normally have good relations, extremists on both sides have committed acts of sectarian terrorism against each other's populations.

Mr. Chaudry said the central government has deployed army rangers, and is seriously concerned over the deteriorating security situation in Karachi.