BAGHDAD — Kurdish security forces took over two major oil fields outside the disputed northern city of Kirkuk before dawn Friday, Iraq's Oil Ministry said, the latest move in a deepening a dispute with the government of Prime Minister Nouri al-Maliki.

Oil Ministry spokesman Assem Jihad denounced the takeover of the Bai Hassan and Kirkuk oil fields as "a violation to the constitution" and warned that it poses "a threat to national unity." He said Kurdish troops moved in and expelled local workers from the two sites.

The seizure of the fields could accelerate the unraveling of already worsening relations between the Kurdish autonomy zone in the north and Iraq's central government. The spat is one of the ripple effects of the Sunni militant offensive that overran much of northern and western Iraq last month, plunging the country into its worst crisis since the last U.S. troops left in 2011.

On Wednesday, al-Maliki accused the Kurds of harboring the Sunni militants. A day later, Baghdad authorities suspended all cargo flights to the Kurdish region's two main airports.

The Kurds responded by declaring their politicians will boycott Cabinet meetings and renewing demands that al-Maliki step down.

The two sides have squabbled for years over a host of issues, chief among them oil rights and land disputes. And yet they have also found room for compromise, and the Kurds have provided critical backing to help al-Maliki become prime minister.

But the Sunni militant blitz led by the Islamic State extremist group has effectively cleaved the country along ethnic and sectarian lines — the swath of militant-held Sunni areas, the Shiite-majority south and center ruled by the Shiite-led government in Baghdad and the Kurdish north. In the process, the Kurds appear increasingly ready to go it alone.

The Kurds, who have long agitated for a state of their own, have pushed into disputed territory, including the oil-rich area of Kirkuk. They say the move aims to protect civilians from the militant onslaught, but the lands they have entered have considerable Kurdish populations, making it unlikely the Kurds would be willing to relinquish them.

The president of the Kurdish area has also urged regional lawmakers to pave the way for a referendum on independence — something Baghdad and the U.S. oppose.

At the same time in Baghdad, national lawmakers are struggling to broker an agreement on a new prime minister, president and speaker of parliament after April elections.

The legislature is scheduled to meet Sunday for its second session amid calls for the quick formation of a new government that can confront the militants and hold the country together.

Al-Maliki, whose State of Law bloc won the most seats in the elections, has shrugged off calls to step aside, vowing to pursue a third consecutive term. His opponents — and many former allies — want him removed, accusing him of monopolizing power during his eight years in office and contributing to the current crisis by failing to promote reconciliation with Sunnis.

The United States and other world powers, as well as Iraq's top Shiite cleric, have pressed for a more inclusive government that Iraqis of all stripes can rally around.

On Friday, Ayatollah Ali al-Sistani again urged lawmakers to move swiftly toward a compromise, calling on them to "rise above selfish aims" and to "speed up the election of the three leadership positions and the formation of a new government accepted by wide national approval to lay the radical solutions to the country's accumulated problems and crises."

"The challenges and the large risks that face Iraq now and in the future threaten civil peace and the unity of the social fabric and forecast a divided and disputed future of Iraq," Abdul-Mahdi al-Karbalaie, a cleric who represents the reclusive al-Sistani, told worshippers in a sermon Friday in the holy city of Karbala.