Kurdish leaders have demanded constitutional guarantees for their northern regions, including self-rule and reversal of the "Arabization" of Kirkuk and other northern areas. Saddam Hussein relocated Iraqi Arabs to the region in a bid to secure the oil fields there.
Politicians had hoped to convene the new parliament by Sunday. But Ali Faisal, of the Shiite Political Council, said the date was now "postponed" and that a new date had not been set.
"The blocs failed to reach an understanding over the formation of the government," said Faisal, whose council is part of the United Iraqi Alliance.
The Kurds, he added, were "the basis of the problem" in the negotiations.
"The Kurds are wary about al-Jaafari's nomination to head the government. They are concerned that a strict Islamic government might be formed," al-Faisal said. "Negotiations and dialogue are ongoing."
In another twist, alliance deputy and former Pentagon favorite Ahmad Chalabi was to meet Thursday with interim Prime Minister Ayad Allawi, whose party won 40 seats in the assembly. It was unclear why the meeting between the two rivals was taking place.
Both Allawi and Chalabi are secular Shiites opposed to making Iraq an Islamic state. Concerns over a possible theocracy are especially pertinent because the main task of the new assembly will be to write a constitution.
Although Kurds make up only about 15 percent of Iraq's population, they won 27 percent of the assembly seats - largely because most Sunni Arabs did not participate in the elections, either to honor a boycott call or because they feared attack by Sunni-led insurgents trying to disrupt the vote.
Sunni Arabs, who comprise about 20 percent of the population, were favored under Saddam's regime, which oppressed the majority Shiite Arabs. Iraqi Kurds are mostly Sunni, but their Kurdish identity is far more significant to them than any tie to Sunni Arabs.
Wednesday's attacks in Baghdad began when a car bomb struck an Iraqi army base, killing eight soldiers and wounding at least 25. A second car bomb an hour later at an army checkpoint killed four soldiers. Separate clashes killed two police officers, the Defense Ministry said.
Also Wednesday, an Internet statement in the name of the Ansar al-Sunnah Army claimed the killing of two Turkish drivers abducted Feb. 25 on the road to Kirkuk, and a Swede of Iraqi descent who was kidnapped last month pleaded for his life in a video left at an international news agency in Baghdad.
It was not possible to verify the authenticity of either the claim or the video.
The latest violence came a day after the killings in Baghdad of an Iraqi judge and his son, both of whom worked for the tribunal that will put Saddam and members of his regime on trial. Three gunmen in a speeding car raked the pair with gunfire as they were trying to get into a vehicle outside their home.
The shootings marked the first time any legal staff working for the Iraqi Special Tribunal have been killed.
On Monday, the tribunal had issued referrals for five former regime members - including one of Saddam's half-brothers - for crimes against humanity. Referrals are similar to indictments, and are the final step before trials can start.
It wasn't clear, however, if the court actions inspired the killings of Judge Barwez Mohammed Mahmoud al-Merwani and his son, lawyer Aryan Barwez al-Merwani. The son was the local head of the Patriotic Union of Kurdistan, one of two parties in the Kurdish coalition.
Judges and other legal staff have not even been identified in public because of concerns for their safety, and tribunal officials have kept a low profile for the same reason.
The Iraqi Special Tribunal was set up in late 2003 after Saddam was toppled. But after five potential candidates were killed, some judges declined calls to work at the court. At least half the tribunal's budget has gone to security.
A court official, who declined to be named, said the slain judge was one of more than 60 investigative, appellate and trial judges working at the court.
Associated Press writers Sameer N. Yacoub, Patrick Quinn, Todd Pitman and Antonio Castaneda in Baghdad contributed to this report. Eric Talmadge contributed from Tokyo.