Iraqi Prime Minister Ibrahim Jaafari has cancelled a meeting with senior political leaders, apparently to protest against a campaign to oust him.
Iraq's politicians have already held months of talks
Kurdish and Sunni Arab leaders are unhappy with Mr Jaafari, and have said they will not join a national unity government with him at its head.
This is the latest crisis to hit attempts to form a new government.
Iraq is undergoing one of its worst periods of violence, with at least 30 people killed in attacks on Thursday.
At least 400 people have been killed since 22 February, when one of Iraq's holiest Shia shrines at Samarra was bombed.
A senior UN official has blamed an "endemic" breakdown of security for the increasing bloodshed.
John Pace, until recently UN human rights chief in Iraq, told the BBC News website that 75% of the hundreds of bodies that arrived at the Baghdad mortuary each month showed signs of torture or execution.
Last month, an investigation was launched into claims by the US military that an Iraqi interior ministry "death squad" has been targeting Sunni Arab Iraqis.
In other developments:
- US forces say they have detained 61 militants linked to al-Qaeda in Iraq leader Abu Musab al-Zarqawi near Falluja
- Members of the Mehdi Army, a militia loyal to radical Shia cleric Moqtada Sadr, take over a key defence role in Baghdad's Sadr City after a minibus bomb there kills at least five people
- Gunmen fire on the car of one of the leaders of Iraq's main Sunni Arab alliance, Sheikh Adnan al-Dulaimi, killing a bodyguard
- At least nine members of the Iraqi security forces die in an attack on a checkpoint near the northern city of Tikrit
- At least four people are killed and 11 wounded when a bomb explodes at a vegetable market in Zafaraniya, south-east Baghdad.
Iraqi political leaders are coming under concerted pressure from world leaders, who believe the failure to form a new government is partly responsible for fuelling the violence.
Mr Jaafari had called the meeting to discuss ways to resolve disagreements and to counter the recent upsurge in sectarian bloodshed.
But the meeting was cancelled without the government giving a reason.
A member of one of his coalition partners, the Kurdistan Alliance, criticised the decision.
"The cancellation of this meeting is a regrettable thing, because such meetings are essential under the current situation," Mahmoud Uthman said.
Mr Uthman suggested the meeting was cancelled because the leaders of the main Kurdish, Sunni Arab and secular parties had asked the Shia-led United Iraqi Alliance to withdraw Mr Jaafari's nomination for the premiership.
"The Kurdish and the Sunni groups think that he is not appropriate, and they cannot form a cabinet with him as he is not neutral," he said.
Mr Jaafari has been widely criticised for poor performance in government.
He has also come under fire for appointing Shia politicians to the main ministries in his government, and for allegedly not intervening to stop the interior ministry from operating secret death squads targeting Sunni Arabs.
But last month the United Iraqi Alliance, which won 128 out of 275 seats in December's parliamentary elections, voted to nominate Mr Jaafari for the premiership.
He beat his nearest rival, Adel Abdel Mahdi of the Supreme Council for the Islamic Revolution in Iraq, by just one vote, largely due to the support of radical Shia cleric Moqtada Sadr.
The Kurdistan Alliance made it clear they opposed the UIA's choice, but they did not stop talks on forming a coalition government.
Mr Jaafari has called for the formation of a national unity government encompassing all of Iraq's ethnic, religious and political groups.