Fighting has broken out between Iraqi government forces and Shia militias on one side and Kurdish militia on the other in Kirkuk:

Iraqi forces clashed with fighters from the Kurdish semiautonomous region in the oil-rich province of Kirkuk early Monday, Iraqi and Kurdish officials said, in a standoff over Kurdish independence that threatens to unravel a multinational coalition battling Islamic State.

There are initial reports of many casualties from this first round of fighting. The Iraqi government assault is being described by Kurdish officials as a “major, multi-pronged” attack, and the Iraqi government claims to have seized “vast areas” in and around the city, but Kurdish officials dispute that. The U.S. has been urging all parties to avoid escalation, but it seems that no one there is paying much attention to what Washington wants at this point.

Now that the fighting has started, it may prove difficult to stop anytime soon. The best thing the U.S. can do is to continue appealing to Baghdad for restraint and warn them that they are jeopardizing relations with Washington if they continue to carry out a military campaign in Kurdistan. Publicly, U.S. officials should emphasize the need for de-escalation, and if at all possible the president should not be allowed to pop off with random threats and insults against anyone involved. The U.S. has limited influence and may not be able to keep the situation from spiraling out of control, but it can try to use what influence it has to pull the different sides back from the brink. Ideally, we would have an administration interested in and capable of conducting sensitive diplomacy with a fully-staffed State Department to cope with this crisis, but since we don’t have any of that we can at least hope that the administration won’t make an already bad situation worse.

Update: There are now reports that Kurdish forces are falling back, and civilians are fleeing the city in large numbers.