Police and military sources said most of the dead were Sunnis and had been killed in the 24 hours since the attack, which destroyed the golden dome of the al-Askari shrine in Samarra, one of Shia Islam's most revered sites.

The Iraqi government has cancelled all police and army leave, extending curfews in Baghdad and other cities in an attempt to prevent the violence from spreading further.

As world leaders including Tony Blair called for Iraqis not to be deflected from the task of establishing a unity government, the main Sunni political party pulled out of talks called by the Iraqi president, Jalal Talabani, in an attempt to avert the descent towards civil war.

The Iraqi Accordance Front accused the ruling Shia of fomenting attacks on civilians and dozens of Sunni mosques in retaliation for the attack on the Shia shrine.

It said it was suspending negotiations with the Shia Alliance over the government's failure to protect Sunni mosques, more than 90 of which have been attacked, and demanded an apology from Shia leaders before rejoining talks.

After discussions with Shia and Kurd groups and leaders of a small Sunni party, Mr Talabani warned that, if civil war came, "no one will be safe".

Mr Blair said those who carried out the bombing - which he claimed was likely to be al-Qaida - wanted to "stop the will of the Iraqi people for the country to come together in a unity government".

"Each time this happens our reaction is not to say let's walk away," he said at his monthly press conference in London. "Our response has to be that we stand up and defeat these people."

The US president, George Bush, condemned the shrine attack as an "evil act" and appealed for restraint, while the UN security council called on Iraqis to rally behind a non-sectarian government.

Police and military sources said there had been more than 130 deaths since yesterday's bombing, most of them Sunnis. The majority of the deaths happened around Baghdad and Basra.

In the worst single incident, 47 people who had taken part in a joint Sunni and Shia demonstration against the Samarra attack were dragged from vehicles as they left and shot dead in Nahrawan, on the outskirts of Baghdad.

Their bodies were dumped in a ditch by the side of the road and found near the village of Nahrawan, south of Baghdad.

Sixteen people - including eight civilians - were killed and 21 injured when a bomb aimed at an army foot patrol exploded in a busy market in Baquba, north-east of Baghdad.

Earlier, one person was killed and two injured when gunmen opened fire on a Sunni mosque in the town.

Iraqi police also reported finding around 50 bodies, many of them with their hands bound, at sites around Baghdad. It was not immediately clear whether this figure included the 47 recovered in Nahrawan.

In Basra, which is predominantly Shia, men dressed in police uniform took 11 Sunni prisoners from a prison. They were later found dead at various sites in the city. Officials put the overall death toll in the city at 25.

An Iraqi journalist working for the al-Arabiya television channel was kidnapped and killed, along with two members of her crew, while reporting on the Samarra attack.

The bodies of Atwar Bahiat, a 26-year-old Sunni who had previously worked for al-Jazeera, her cameraman, Adnan Khairallah, and her soundman, Khaled Mohsen, were found on the outskirts of the town.

The US military said seven US soldiers had been killed in two separate bomb attacks north of Baghdad.

The wave of violence came as Iraq's various factions struggled to agree on the formation of a government after elections for the country's first full-term parliament on December 15. They have until mid-May to form a new government.

Talks between the main Shia, Sunni and Kurdish political parties were already stumbling, and yesterday's attack and the ensuing violence have brought deadlock.

A statement posted on the internet by the Mujahideen Council, which includes the group al-Qaida in Iraq, blamed Shia leaders for blowing up the mosque in order to justify attacks.

The Sunni Muslim Clerics Association accused its Shia counterparts of supporting violence, saying 184 Sunni mosques had been damaged, 10 clerics killed and 15 abducted.

The president of Iran, Mahmoud Ahmadinejad, blamed the US and Israel for the bombing of the shrine, saying it was the work of "defeated Zionists and occupiers".