It was the deadliest single incident in the Iraqi capital for six months, but there was nothing unique about the explosion; it took place a few hundred metres from Haifa Street, a well-known centre of resistance to the American occupation and the scene of heavy fighting on Sunday. It was embarrassingly close to the green zone and the US embassy.

But it reveals a grim truth about the nature of Iraq's evolving insurgency: Iraqis are killing Iraqis.

In recent months, and especially since the handover of "power" to the unelected interim government, Iraq's resistance has concentrated its efforts on killing those who collaborate with the Americans - the police officers, would-be police officers, translators, governors and government officials.

It is beginning to look like, and feel like, civil war.