It appears that Nouri al Maliki is looking at enforcing his Shia vision of Iraq on the city of Mosul, and the Kurds living there are not amused:

The Shiite-led government of Prime Minister Nuri Kamal al-Maliki is squeezing out Kurdish units of the Iraqi Army from Mosul, sending the national police and army from Baghdad and trying to forge alliances with Sunni Arab hard-liners in the province, who have deep-seated feuds with the Kurdistan Regional Government led by Massoud Barzani.

It looks like the US military will take no actions if a conflict breaks out.

Iraq, the gift that just keeps giving.