From the Washington Post:
Hundreds of Shiite Muslim militiamen have deployed in recent weeks to this restive city — widely considered the most likely flash point for an Iraqi civil war — vowing to fight any attempt to shift control over Kirkuk to the Kurdish-governed north, according to U.S. commanders and diplomats, local police and politicians.
Until recently, the presence of the militias here was minimal. U.S. officials have called the Shiite armed groups the deadliest threat to security in much of the country. They have been blamed for hundreds of killings during mounting sectarian violence in central and southern Iraq since the bombing of a revered Shiite shrine in February.
Here.