BAGHDAD – Car bombs hit three Shiite cities in southern Iraq on Monday, killing more than 20 people in an apparent move to derail progress toward forming a new government as political leaders tried to break the eight-month deadlock.

The blasts in the holy cities of Karbala and Najaf and in Iraq’s second-largest city of Basra were the third major attacks since last week, after the slaughter of more than 50 Christians in a Baghdad church and a string of 13 coordinated bombings across Baghdad that killed more than 90 people.

There was no claim of responsibility for Monday’s attacks, but the violence underscores the desire of al-Qaida and other Sunni extremists to foment sectarian division at a time when Iraqis are watching to see if their leaders can form a new government accepted by both the Shiite majority and the Sunni minority.

In the northern town of Irbil, leaders of Iraq’s major political blocs met Monday for the first time since parliamentary elections in March. The 90-minute televised session, the start of three days of talks, did not lead to a breakthrough.

The battle is largely a contest between the Iranian-favored coalition of Shiite Prime Minister Nouri al-Maliki along with followers of anti-American cleric Muqtada al-Sadr against a Sunni-backed secular coalition led by former Prime Minister Ayad Allawi.

At stake is whether Iraq has an inclusive government of both the majority Shiites and the minority Sunnis or a Shiite-dominated government with the Sunnis largely in opposition — a recipe that many worry will turn the country back to the sectarian violence of a few years ago.

Al-Maliki’s bloc won 89 seats in the March 7 election compared to 91 for Allawi’s coalition; neither side won a majority of seats needed to govern.

Recently, momentum has moved in al-Maliki’s direction. After gaining the support of al-Sadr, who used to be one of al-Maliki’s staunchest opponents, he also picked up the support of a smaller coalition this weekend.

And the Kurds, who rule the three northern Iraqi provinces, are thought to support al-Maliki’s re-election bid as long as President Jalal Talabani, a Kurd, is allowed to stay in office.

Officials in Allawi’s Iraqiya coalition said Monday that they were still demanding the prime minister’s office, but an international observer with knowledge of the talks said there is grudging acceptance within Iraqiya that al-Maliki will keep his position. He did not want to be identified because of the sensitivity of the ongoing talks.

Officials familiar with the talks say Iraqiya is pushing for limits to al-Maliki’s power should they join forces with him and that Allawi is rejecting a proposed role of parliament speaker in an al-Maliki government.