The spiralling violence threatens to derail negotiations on setting up a government of national unity, with the main Sunni political party declaring a boycott of talks with the Shia-led government over the reprisal attacks.

The main Sunni alliance, the National Concord Front, also boycotted an emergency meeting of national leaders held by President Jalal Talabani in a bid to restore calm.

"To put out the fire is a holy duty and will be achieved through national unity," Talabani told reporters after the meeting.

The surge in sectarian violence follows the bombing Wednesday morning of a Shia shrine in Samarra, north of Baghdad, and reprisals against Sunni mosques nationwide.

Eighty bullet-riddled corpses were brought to the Baghdad morgue between Wednesday afternoon and Thursday morning, the deputy director of the morgue, Doctor Kais Mohammed, told AFP.

"I've only been able to carry out autopsies on 25 of them," he said, adding that all had been shot. Many of the bodies, which were dumped in Baghdad and its suburbs, could not immediately be identified, but they were widely believed to be those of Sunnis.

Another 47 bodies of men shot to death were discovered along with 10 burned out cars alongside a road near Nahrawan, southeast of Baghdad, police said.

The corpses were found near a brick factory and it was not immediately known if the victims were workers from the factory.

One Sunni was also killed Thursday and two wounded in a drive by shooting outside a Sunni mosque in Baquba, northeast of the capital, and a Sunni sheikh was shot dead in Hillah, south of Baghdad, police said.

Iraq has placed its security forces on high alert and cancelled all leave. The night curfew in Baghdad was brought forward from 11:00 pm to 8:00 pm on Wednesday.

The upsurge in killings came after suspected al-Qaeda linked militants bombed the 1,000-year-old Imam Ali al-Hadi mausoleum, one of the countries' main Shia shrines, in the town of Samarra, north of Baghdad.

Early Thursday police also reported finding the bodies of three Iraqi journalists working for Dubai-based Arabiya satellite television who were kidnapped near Samarra Wednesday evening while reporting on the shrine bombing.

"The bodies of the presenter Atwar Bahjat, of cameraman Adnan Abdallah and of soundman Khaled Mohsen were found early this morning some 15km north of Samarra," police said.

In other violence, at least 12 people were killed in a powerful roadside bomb attack in Baquba, 60km northeast of Baghdad, of which eight were Iraqi army soldiers and four other civilians, police said, adding 20 others were wounded. Ayatollah Ali al-Sistani, renewed calls to his community to remain calm and forsake revenge for the bombing of the shrine.