WASHINGTON, Dec 19: The day new US Defence Secretary Robert Gates took office, the Pentagon issued a quarterly report acknowledging that ‘insurgents’ in Iraq had achieved a ‘strategic success’ by unleashing a spiral of sectarian killings.

The 50-page report, mandated quarterly by Congress, paints a bleak picture, warning that increased violence threatens the political institutions that United States has set up since 2003 when it invaded Iraq.

The rapid spread of violence this year has thrown the government's future into jeopardy, Pentagon officials said. Unlike previous reports, the Pentagon’s latest assessment of the situation on the ground omitted any explicit statement that Iraq is not in a civil war.

The report on “Measuring Stability and Security in Iraq” cites a 22 per cent increase in attacks, to nearly 1,000 per week. It says two thirds of the attacks are aimed at coalition forces, but that the remaining attacks, on Iraqi security forces and civilians, are much more deadly.

Attack levels in Iraq hit record highs in all categories nationwide but Iraqi civilian casualties have increased manifold. Since January, ethno-sectarian executions rose from 180 to 1,028 in October, and ethno-sectarian incidents rose from 63 to 996 over the same period.

The number of US and coalition casualties surged 32 per cent from mid-August to mid-November, compared with the previous three months, the report said. Over the same period, the number of attacks per week rose 22 per cent, from 784 to 959.

The Pentagon says that most of the violence is limited to Baghdad and three other provinces -- Anbar, Salah a-Din and Diyala -- but that 37 per cent of the Iraqi people live in those areas.

The report blames sectarian militias for most of the violence, singling out the Mahdi Army of Shia cleric Moqtada al-Sadr for having what it calls "the greatest negative effect on the security situation in Iraq.”

It says the militia has replaced al-Qaeda terrorists as the biggest cause of civilian casualties in Iraq, and has become the greatest threat to the coalition. It calls the Mahdi Army Iraq's "most dangerous accelerant of potentially self-sustaining sectarian violence."

“The violence has escalated at an unbelievably rapid pace," said Marine Lt-Gen John F. Sattler, director of strategic plans and policy for the Joint Chiefs of Staff, while briefing journalists on the report.

Assistant Secretary of Defence Peter Rodman said the sectarian violence was the result of the bombing of a Shia shrine in the Iraqi city of Samara in February.

Subtracting those Iraqi forces killed and wounded, and those who have quit the force, only 280,000 are available for duty.