Iraq's interim government says talks to end the standoff in the holy city of Najaf have collapsed. A tense cease-fire had been in place as the negotiations took place. Elsewhere, U.S. and Iraqi officials say about 90 insurgents have been killed in airstrikes and fighting in the cities of Samarra and Hilla.

Iraqi government officials had been holding talks since early Friday with radical Shiite cleric Moqtada al-Sadr and his militia, the Mahdi army, in a bid to restore peace to one of the holiest cities in Shiite Islam, after a week-and-a-half of bitter fighting.

But the interim government's national security adviser, Mouffaq al-Rubaie, told reporters the talks have failed. "I am very sad to announce the failure of the effort of this government to solve the Najaf crisis peacefully," he said. "The Iraqi interim government has exhausted all efforts and did not leave any stone unturned to reach a peaceful conclusion to this crisis. The Iraqi interim government is resuming military clearing operations to return the city of Najaf to normal city functions, and to establish the law and order in this holy city."

Thousands of demonstrators have trekked to Najaf to protest the fighting near the Shrine of Imam Ali. The shrine is one of the holiest sites to Shia Muslims worldwide, and is also considered sacred by Sunnis. The fighting has angered many followers of both sects, even those who do not necessarily support Mr. al-Sadr.

Hundreds of people have been killed in the battle for control of Najaf, and the unrest spread to a number of other cities in the Shia-dominated south. The talks brought a two-day lull in the fighting.

In Baghdad, meanwhile, the interim government has invited more than 1300 delegates to attend a key national conference. They will spend two or three days deciding on the members of a new interim National Council, which will serve as a watchdog on the government.

The conference has already been delayed two weeks at the request of the United Nations, which is helping organize it. Several influential groups, including Mr. Sadr's and a major Sunni organization, have said they intend to boycott the meeting, and the organizers wanted more time to convince them to take part.

The man in charge of the conference, Fu'ad Masoum, told reporters they have not had much luck, but he downplayed the overall significance of their absence.

"No conference would lose legitimacy because some parties have boycotted it," he said. "The majority of those attending the conference represent the Iraqi people, and the movements that boycott this conference are free to do that. This does not cause the conference to lose its legitimacy."

An adviser to the United Nations said Mr. al-Sadr and the other groups expected to boycott have been issued invitations anyway, and seats will be reserved for them at the meeting.

The national council will consist of 100 people, but only 81 of them will be chosen over the next few days. The other 19 will be former members of the Iraqi Governing Council, who were automatically granted membership. The U.N. official says the national council must reflect the diversity of Iraqi society, and will include members from every province, religion, ethnic group and, in his words, political current.

The council will not have legislative powers, but it will be able to overrule some decisions of the Cabinet by a two-thirds vote.