Baghdad: Militants blew up two minarets of a revered Shi'ite mosque in the Iraqi city of Samarra on Wednesday, targeting a shrine that had already been badly damaged in a 2006 attack, Shi'ite officials said.

One witness said the minarets at Samarra's Golden Mosque had been largely destroyed. The attack on the mosque last year was a turning point in Iraq, sparking a wave of sectarian violence that has killed tens of thousands of people and pushed the country to the brink of all-out civil war.

"The explosion targeted the two golden minarets. They have been damaged ... This is a criminal act which aims at creating sectarian strife," Saleh Al Haidari, the head of the Shi'ite endowment in Iraq, a major religious body, told Reuters.

He blamed "extremists" for the attack. It was unclear exactly how the minarets had been blown up, but residents said there had been clashes between gunmen and police in the area before the blast, which occurred around 9.00 a.m.

A senior Iraqi government official said the attack was "very bad news for Iraq".

The Golden Mosque is one of the four major Shi'ite shrines in Iraq. Samarra, north of Baghdad, is a predominantly Sunni city. Other major sites are in the holy Shi'ite cities of Najaf and Kerbala and the Baghdad district of Kadhimiya, also mainly home to Shi'ites.

Two of the 12 revered Shi'ite imams are buried in the Samarra shrine -- Imam Ali Al Hadi, who died in 868 and his son, the 11th imam, Hasan Al Askari, who died in 874.

Police and the senior government official said the Shi'ite-dominated Interior Ministry had been responsible for security at the mosque. Police said the ministry took over from local security forces in April.

"We know that two weeks ago there was an attempt to also target it, but it was foiled," the official said.

Asked how it could have been attacked with the Interior Ministry in charge of security, the official said: "Apparently the force was not enough".

US military officials have accused Al Qaida of trying to ignite sectarian tensions by attacking Shi'ite targets. There have been several large car bombings in key Shi'ite cities in southern Iraq in recent months.