For hundreds of faithful gathered at the historic Mecca Masjid, it turned out to be a black Friday as a powerful bomb ripped through the premises, killing at least 12 persons and triggering tension in the communally-sensitive old city areas.

Ahmed, who is undergoing treatment for his injuries at Osmania General Hospital, was among nearly 6,000 people who were offering afternoon prayers at the 400-year-old mosque when the tragedy struck.

"I was offering prayer when I heard a huge explosion. Initially, I thought it could be a cracker but I soon realised it was a bomb blast," Rasheed Ahmed, a tourist from Maharashtra, said.

The blood spilled over the 'wazu khana' (water tank), where Muslims perform ablution before offering prayers, as the crude bomb went off at 1.20 pm. Pieces of human flesh, slippers and caps were strewn around the blast site.      

The policemen, who arrived at the spot minutes after the explosion, had to face the wrath of people who went berserk attacking buses, petrol bunks and other public properties.

As the incident triggered frayed tempers and spontaneous demonstrations, tension prevailed in old city areas, including Charminar, Moghulpura, Lal Darwaza, Gowlipura and Mehdipatnam.

"When the Friday prayers were about to conclude, we heard a big sound. Initially, we thought it was a tyre burst outside. However, soon we soon realized that it was a bomb explosion," Aijaz Ahmed said.

Another eyewitness Rafiq Ahmed said soon after the blast that there was panic all around but the Imam of the mosque tried to calm them down.

"When I rushed out, I saw parts of human bodies strewn around and the injured were being shifted in ambulances," Rafiq said.

"I was praying inside the main mosque when the blast occurred. The people were engaged in Sunnat Namaz, which is prayed individually, before the main Namaz with the congregation. The blast was like a huge 'pop' sounding very much like a transformer blow out," Abdaal Akthar said.

Ambulances rushed to the spot minutes after the blast and the injured were taken to Osmania General Hospital and other private hospitals in the area.

Eyewitnesses alleged security near the mosque was lax and no frisking was done before allowing the people inside.      

The police recovered a mobile phone from the site which was believed to have been used to trigger the blast.

"It appears to be a crude bomb," state Director General of Police M A Basith told media persons. Two more live bombs were recovered and defused by the police.

Mecca Masjid, built in 1670, is one of the oldest mosques in the country and is located near the historic Charminar, the cultural symbol of Hyderabad. It is called the Mecca Masjid because its central arch is believed to contain bricks brought from the holy city of Mecca.

It took over 75 years to build the grand mosque. The construction had started during the regime of Mohammad Quli Qutb Shah, the sixth Sultan of Hyderabad and completed by Mughal Emperor Aurangzeb.