BAGHDAD, Iraq, April 14 — An Iranian government delegation arrived in Baghdad on Wednesday to help mediate the standoff between American troops and a rebel Shiite cleric holed up in Najaf with hundreds of his militiamen, offering American officials an improbable ally in their quest to put Iraq on a peaceful path to self-government.
As political momentum built against the cleric, Moktada al-Sadr, the hostage-taking crisis that erupted as he began his insurrection 11 days ago took a savage turn with the announcement by Italy's foreign minister, Franco Frattini, that one of four Italian security guards seized in an ambush near Falluja earlier in the week had been killed.
Mr. Frattini said the killing had been confirmed by Italy's ambassador in Qatar, headquarters for Al Jazeera television network, after the diplomat had been shown a videotape of the killing, which the satellite channel said it would not broadcast because it was "too bloody."
Most of southern Iraq has quieted, but fighting has continued to flare in the Sunni city of Falluja, west of Baghdad, where American marines on Wednesday entered the sixth day of a cease-fire that has been repeatedly broken by heavy exchanges of rocket, mortar and small-arms fire, as well as by strikes from American combat jets and attack helicopters.
Also on Wednesday, Lakhdar Brahimi, the United Nations special envoy, ended an 11-day visit to Iraq by outlining the beginnings of a plan — he called it a "sketch" — for a transition to Iraqi sovereignty, one that suggested a weaker continuing role for the United States than the Bush administration has envisioned.
Among other things, he suggested that the Iraqi Governing Council, the American-appointed advisory body seen by United States officials as the most viable nucleus of a transitional government after June 30, should "cease to exist" on that date.
As the five-man delegation from Iran's Foreign Ministry settled into a Baghdad hotel on Wednesday, American officials in Baghdad and Washington said it was here at Britain's suggestion, although they said the United States had consented to the visit.
Some American officials saluted what they saw as a rare instance of cooperation in 25 years of enmity between Washington and Tehran — even if the Iranians intended to extend Iran's influence as well as broker a peace.
The situation was also odd for Iran and Iraq, which fought each other to a stalemate in their eight-year war in the 1980's. That conflict was prompted in part by Saddam Hussein's fears that Iraq's Shiite majority, about 60 percent of the country's population, would be influenced by Iran's militant form of Shiite Islam. That fear is a current one among some American officials and much of Iraq's Sunni minority.
The Iranian delegation held no formal meetings on Wednesday. It was headed by Hossein Sadeghi, the Foreign Ministry's director of Persian Gulf affairs. In remarks to reporters, he played down the delegation's role, saying it would be one not of mediation, but of gaining "a better understanding of what's going on in Iraq."
But the Iranian foreign minister, Kamal Kharrazi, said earlier in Tehran that the delegation was responding to an appeal for assistance and would do all it could to end the crisis.
An earlier hint of Iran's willingness to help head off more turmoil in Iraq came in remarks on Saturday by Iran's president, Mohammad Khatami. Greeting a visiting Iraqi official, he indirectly criticized the uprising led by Mr. Sadr, saying, "Iran considers any policy that would intensify the crisis in Iraq and jeopardize the establishment of security harmful for Shiites and Islam."
There were already signs that Mr. Sadr — who has been under pressure from a group of powerful Najaf-based clerics who have close ties with Iran — was moving away from confrontation. He announced on Wednesday that he had dropped all conditions for negotiating with the Americans.
Aides to Mr. Sadr told reporters that he would no longer insist that American troops leave Najaf, a Shiite holy city about 110 miles south of Baghdad, before his own militiamen did, and that he would no longer demand that the Americans free thousands of detainees. Haidar Aziz, a spokesman in Baghdad for Mr. Sadr's Mahdi Army, said the cleric had decided to turn the militia into "a political and social organization with no military activities."
Finally, the aides said, Mr. Sadr had agreed to submit to a warrant for his arrest in the murder of a rival Shiite cleric last year, but only "after the formation of a legitimate and sovereign government" — meaning after American control of Iraq ends.
American commanders said they would wait to see whether Mr. Sadr's actions matched those statements, and a 2,500-man American military task force backed by attack helicopters tightened its grip on the approaches to Najaf. But the commitments the aides outlined appeared to tally closely with demands put to him at a crisis meeting on Monday night by a group representing the country's most influential ayatollahs. That group included Ali al-Sistani, the Iranian-born cleric who has emerged as the most powerful voice among Iraq's religious Shiites.
Although Ayatollah Sistani has refused to meet American officials and has been increasingly critical of American plans for a transition to Iraqi rule, he has also stressed the importance of securing Shiite majority rule peacefully — a principle violated by Mr. Sadr.
The uprisings reached their greatest intensity across Iraq two weeks ago, just as Mr. Brahimi, the United Nations envoy, arrived to begin weighing Iraqis' opinions about a transition plan. Despite the added difficulties the fighting posed to that mission, Mr. Brahimi said, he had formed a "few still tentative ideas" about how to move Iraq forward toward the first elected government in its history by January.
Mr. Brahimi suggested that some of the Governing Council's 25 members could be appointed to other government jobs, and that the transitional government might be formed from scratch, "led by a prime minister and comprising Iraqi men and women known for their honesty, integrity and competence."
Many Iraqis dismiss the council as unrepresentative, or too closely identified with the occupiers.
Mr. Brahimi also spoke of holding "a large national conference," possibly as early as July this year, to promote "national dialogue, consensus-building and national reconciliation," and said it should elect a consultative assembly to work with the transitional government.
The idea mirrors the recent political rebuilding process in Afghanistan, where Mr. Brahimi served as the United Nations' special envoy.
Marking his distance from the Americans, he went further than on any previous occasion in criticizing the occupation.
"I believe that what we have heard in Iraq from everybody, and from the Americans themselves, is that there is no military solution to the problems, and that the use of force, especially the excessive use of force, makes matters worse and does not solve the problem," Mr. Brahimi said.
In response to a reporter's question about reports of American soldiers' abusing Iraqis, he added: "No one should look at Iraqis as if Iraqis do not deserve respect. We do not accept this from any state or any person."
Before the killing of the Italian contractor, Fabrizio Quattrochi, became known, Italy's prime minister, Silvio Berlusconi, who visited Italian troops in southern Iraq last weekend, ordered a military plane sent to Baghdad to evacuate Italian citizens who could reach the capital, including Italian journalists.
The move was the most dramatic yet by any of the nations that has citizens among more than 20 hostages who have been seized in the last week and not released. They include seven American contractors and two American soldiers seized with them off an American military fuel convoy, as well as three Japanese, the three Italians seized with Mr. Quatrocchi, three Czechs, a Canadian, and an Israeli Arab.
There was no new information about unconfirmed reports of four bodies found near a highway at Abu Ghraib, where a fuel convoy was attacked last week.
The American arm's-length position on the Iranian mediator was consistent with its policy since last summer, when American intelligence experts said groups or individuals in Iran were responsible for the bombings in May of residential compounds in Saudi Arabia.
Since then, the United States has continued to accuse Iran of supporting Hezbollah, the violent militant group in Lebanon, and of aspiring to develop nuclear weapons. The Bush administration has tried without success to bring the nuclear issue before the United Nations.
Opposing a policy of confrontation, Britain has joined with France and Germany to try to use diplomacy to get Iran to cooperate in dismantling its nuclear arms programs. American officials said Wednesday that the British invitation to Iran over Iraq was an extension of that approach.
"If the British invitation results in something, that would be good," said an administration official, adding that he was not sure if it would.
Other administration officials acknowledge, meanwhile, that there was a vigorous debate among Mr. Bush's aides over whether Iran — which Mr. Bush included with Iraq and North Korea as an "axis of evil" two years ago — was playing a constructive role in Iraq.
Nazila Fathi contributed reporting from Tehran for this article, and Steven R. Weisman from Washington.