The New York Times reports that the Kurds in Iraq have approved a constitution (two weeks ago) that lays claim to the disputed and oil-rich Al-Ta'mim province (home to Kirkuk). This basically stomps right through quiet negotiations that had apparently started recently between Kurdish and Iraqi lawmakers, organized by the United Nations and United States.
The background to this story is fairly straightforward: the Kurds have been getting screwed for a long time, and god damn it, they're not gonna take it anymore!
In a sane world, the historically Kurdish region at the junction of Turkey, Syria, Iraq, Iran and Armenia would be an autonomous Kurdish country. Instead, it's divided. But Iraq's constitution combined the provinces of Suleimaniya, Erbil and Dahuk into the Kurdistan Regional Government, Iraq's only autonomous federal state.
So Iraq (and America) gave the Kurds an inch, and now the Kurds want a mile. But in this case, maybe they deserve it. The Kurds have long claimed Kirkuk and the surrounding areas for themselves. And for decades, they've suffered attempts to violently or coercively reduce their population in the area (see: Saddam Hussein's Anfal Campaign).
Iraq's constitution purposefully left the question of Kirkuk open to a referendum, wherein the people will decide whether to annex themselves into Kurdistan. The recent vote on the constitution is a pre-emptive declaration by the Kurds that Kirkuk (and Al-Ta'mim) belong to them.