From the BBC:
The two minarets of the al-Askari shrine in Iraq, one of the holiest sites in Shia Islam, have been damaged by two explosions, officials say.
According to witnesses the minarets collapsed completely after being hit by bomb blasts around 0900 (0500 GMT).
The shrine houses one of two tombs in Samarra for revered Shia imams.
The bombing of the dome at the mosque in 2006 is widely believed to have set off a continuing spiral of sectarian violence in which many thousands died.
The BBC's Jim Muir in Baghdad says there are obvious fears now that this might give it yet further impetus.