Prime Minister Nouri al-Maliki's government is struggling to repel advances led by militants of the Islamic State of Iraq and the Levant, a well-trained and mobile force thought to have some 10,000 fighters inside Iraq.
The response by government forces has so far been far short of a counteroffensive, restricted mostly to areas where Shiites are in danger of falling prey to the Sunni extremists or around a major Shiite shrine north of Baghdad.
Shiite militias responding to a call to arms by Iraq's top cleric are also focused on protecting the capital and Shiite shrines, while Kurdish fighters have grabbed a long-coveted oil-rich city outside their self-ruled territory, ostensibly to defend it from the al-Qaeda breakaway group.
Government forces backed by helicopter gunships have fought for a week to defend Iraq's largest oil refinery in Beiji, north of Baghdad.
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Militants attacked the site again early today but were beaten back by government forces, said Col. Ali al-Quraishi, the commander of Iraqi counterterror forces at the scene. He said his men exchanged fire with insurgents when they tried to attack a nearby oil pipeline, wounding one solider.
Iran, which has strong ties with Iraq's Shiite-led government, has boosted border security amid advances by the militants.