BAGHDAD - Iraqi Prime Minister Nouri al-Maliki delayed the announcement of a new national unity government Monday amid signs that his recently revived alliance with the anti-American cleric Moqtada al-Sadr might be starting to crack.

Lawmakers had gathered at parliament in the expectation that Maliki would announce at least a partial cabinet, as his aides had promised, putting an end to a political impasse that has paralyzed Iraq for nine months.

But bickering within the political blocs over whom to name to cabinets post forced a postponement of the announcement at least until Tuesday.

The Sadrist faction, which controls 39 seats in the parliament, also objected to plans by Maliki to defer appointments to the sensitive and powerful ministries of defense, interior and national security. Instead, Maliki said at a news conference that he will take charge of the three positions, on an interim basis, until there is agreement among the factions on permanent candidates.

Adnan al-Asadi, the deputy interior minister and a member of Maliki's Dawa party, said the prime minister plans to control the security ministries for up to three months pending a final decision.

Sadrists threatened to boycott any government that did not include appointments to the three ministries, saying they feared that Maliki would take advantage of the temporary measure to consolidate his power within the security forces.

"It is an attempt by him to control the security agencies because he is afraid and he doesn't trust the other factions," said Sadrist lawmaker Amir al-Kinani. "This is evidence that he doesn't have goodwill."

The dispute goes to the heart of a long-standing feud between Maliki and the Sadrists, whose power in Iraq was dramatically curtailed after the prime minister used his security forces to crush their Mahdi Army militia in 2008.

The Sadrists had been resolutely opposed to a second term for Maliki until, in a surprise turnabout, Sadr agreed to back him in October under the terms of a deal brokered by Iran, breaking the ice on the long-deadlocked negotiations and paving the way for the incumbent to keep his job.

But many Sadrists were openly dismayed by the agreement and have said privately that they continue to oppose a second term for Maliki.

The United States was also troubled that the Sadrists had emerged as the deal-breakers in the government negotiations, and U.S. Embassy officials have expressed concerns that the Sadrists will receive powerful positions in the new cabinet.

A Sadrist boycott would dash Maliki's hopes of leading a government grouping all of Iraq's factions and ushering in what Iraqi politicians are hailing as a new era of reconciliation.

"We will not let them withdraw," Maliki told reporters. "We don't want anybody to be out of the government."

The mostly Sunni Iraqiya bloc and the Kurdish alliance said they had reached agreement with Maliki on their nominations to the new cabinet, and a session of parliament was scheduled for Tuesday to announce the lineup.

Some Iraqiya and Kurdish legislators speculated that the Sadrist boycott threats were triggered in part by indications that Maliki would not give the Sadrists one of the three coveted deputy prime minister slots.

But others said they shared the Sadrists' concerns about Maliki assuming temporary control of the security ministries.

"I am worried, too. I don't like it," said independent Kurdish legislator Mahmoud Othman. "Everybody complained in the past that he was trying to control the security forces, that he works alone, and this is a continuation of the same story."