BAGHDAD, Iraq, (By Robert F. Worth and Sabrina Tavernise, NYTimes) October 6, 2005 — Insurgents struck in two separate incidents today, killing at least 10 Iraqis in a suicide bombing in Baghdad and shooting another five in the Northern city of Kirkuk, in what has become an escalating campaign of violence ahead of the Oct. 15 referendum on a new constitution.

The latest attacks come a day after a bomb tore through a Shiite mosque in Hilla, south of Baghdad, killing at least 25 people and wounding more than 87.

Earlier this week, a senior American commander warned that insurgents appeared to be planning to disrupt the referendum with a "spectacular attack or a series of spectacular attacks between the 10th and the 15th of October" in Baghdad.

Capt. Mohammed Ali of the Iraqi police force said that the blast in Baghdad today took place near the oil ministry and that the victims included children, one woman and several students of the nearby police academy. Eleven people were wounded. Around 1:10 p.m. a man wearing an explosive belt boarded a red mini bus headed for Sadr City and other Shiite neighborhoods in Baghdad and blew himself up just after the bus passed the academy, Captain Ali said.

Eyewitnesses described a scene of destruction, with the bus completely burned out and body parts, including the suicide bomber's head, strewn across the site.

"I often see the students of the academy going home from this place," said Hassan Jassim, 23, a worker, who was getting off a bus on the opposite side of the street when the bomb went off. "I saw people dying."

In a separate incident in Baghdad, an interior ministry official said, police patrols followed a car without registration and ended up exchanging gunfire with the two men inside it, killing them both. The official said the patrol discovered that the Opel was a car bomb, and a team of experts was called to the scene to defuse it. The event took place near University of Technology South Baghdad. Outside the northern city of Kirkuk gunmen shot five members of the Iraqi oil protection force, one day after a bomb explosion seriously injured six guards of the Kirkuk-based North Oil Company.

Also today, the American military said one soldier was killed when a patrol struck an improvised explosive device while conducting offense combat operations in north Baghdad this morning.

Meanwhile, thousands of American troops in the Euphrates Valley in western Iraq continued their efforts to cut off insurgent supply routes from neighboring Syria.

The latest violence comes a day after the National Assembly voted to cancel a last-minute rule change that would have made it almost impossible for Iraq's new constitution to fail in the coming referendum.

United Nations officials in Baghdad had warned Shiite and Kurdish leaders that the rule, passed on Sunday, was a violation of international election standards, and could prompt the organization to withdraw from supervising the vote. Sunni Arab leaders who oppose the constitution had also criticized the rule change, saying it amounted to rigging the referendum.

The Shiite and Kurdish leaders capitulated Wednesday, with 119 of 147 lawmakers present voting to cancel the rule change. But Shiite leaders said they were still deeply concerned about whether the vote would be fair, and they reserved the right to challenge the results if the constitution failed in the vote, on Oct. 15.

The dispute has sharpened sectarian divisions over the constitution, and the uneasy resolution seemed to open the door to further dissent, especially if violence worsens. The referendum is a key moment in Iraq's transition to full independence, and the constitution - if approved - would pave the way to the election of a government in December.

In Washington the State Department spokesman, Sean McCormack, called the reversal "a positive step." He said Secretary of State Condoleezza Rice had not made any calls on the matter, but other American officials said the United States helped orchestrate international pressure.

The dispute began Sunday when Parliament quietly adopted new rules stating that the constitution would fail only if two-thirds of registered voters - rather than two-thirds of those actually casting ballots - rejected it in at least 3 of the 18 provinces.

The Shiite leaders said they feared insurgents might manipulate the vote by attacking Shiites to keep them away from the polls. They said they had agreed to cancel the rule change only on condition that the Iraqi government prevent that from happening.

The reversal in Parliament was a relief to Sunni leaders, who had threatened to boycott the referendum after hearing of the rule change. But many remained angry. "We've had a little fiasco in the National Assembly," said Sadoon al-Zubaidy, a Sunni representative who was on the constitutional committee. "It seems to be over."

The dispute was a setback for American officials, who have been trying hard to persuade Sunni Arabs to vote for the constitution. The Americans have also been trying to persuade the Shiite and Kurdish leaders to agree to last-minute changes that might help placate the Sunnis. That effort now seems unlikely to succeed.

Some independent political figures also called the drama an embarrassment for the fledgling Parliament. Most members appear to have voted Sunday without clearly understanding what they were voting for, and then reversed themselves on the orders of their party leaders , who were themselves taking orders from the United Nations.

"They told us, please don't discuss this or make objections, just vote for the statement," Shatha al-Musawi, a Shiite lawmaker, said of the Shiite leadership.

Shiite and Kurdish lawmakers said they were concerned that if insurgent violence led to a low turnout, a small number of people in three provinces could overturn the document even if much greater numbers elsewhere supported it. But their change would have raised the bar for the document's opponents so high that passage would have been almost guaranteed.

The change also designated two different meanings for the word "voters" in a single passage of Iraq's transitional law where the word appears to mean the same thing. The United Nations said the new rules violated international election standards and pressed Shiite and Kurdish leaders to reconsider it.

The power of the United Nations' suggestion became clear during the deliberations on Wednesday, when Hussein al-Shahristani, the acting speaker and a Shiite, made a slip of the tongue.

He called on legislators to consider "the demand - I mean, the proposal - of the United Nations."

Sami al-Askari, another Shiite lawmaker, responded angrily that the United Nations had no right to interfere, and that changing the wording back would be tantamount to giving in to suicide bombers.

"We are now in a test," he said. "Will the United Nations' will win, or the will of the National Assembly? Do we surrender to the terrorists?"

A United Nations official in Baghdad acknowledged that the organization had made a "very strong statement" to Shiite and Kurdish leaders on Tuesday, telling them the rule change "would have put the U.N. in a position not to be able to help in the electoral process." The official spoke on condition that he not be named, citing the delicacy of the talks.

After the vote on Wednesday, Mr. Shahristani made clear that Shiite leaders remained deeply concerned not merely about general violence during the vote, but about the possibility that insurgents would distort the outcome by selectively attacking Shiite areas. He cited threatening leaflets being distributed in Balad, a Shiite town, by the group Al Qaeda in Mesopotamia.

Many Sunnis have raised parallel concerns about military operations in Sunni-dominated areas, sometimes accusing the American and Iraqi military of using violence to prevent Sunnis from voting against the constitution.

Several Iraqi legislators said the whole crisis derived from a flaw in Iraq's transitional law, which was written in 2003 under the American occupation. The passage in question was included at the insistence of the Kurds. They are the majority in three Iraqi provinces, and they drew up the provision to ensure that they could vote down a constitution they disapproved of.

Shiite civilians were the target of the bomb in Hilla, 60 miles south of Baghdad. It detonated just outside a mosque at about 5:30 p.m., as worshipers gathered to begin Ramadan, police officials said. The blast sheared the facade off the mosque and brought down a second wall. At least 25 people were reported killed and 87 wounded. The death toll is expected to rise, according to a Hilla police official, who declined to give his name because he was not authorized to speak to reporters.

The mosque was particularly crowded for a funeral of a Shiite restaurant owner who had been killed when an insurgent put a bomb in a cassette player and left it in the restaurant. The police had blocked the streets around the mosque to protect against suicide car bombs, but Wednesday's attackers circumvented the blocks and left the bomb at the gate, the police official said.

In the darkness, rescue workers and residents dug frantically through the rubble, looking for bodies. In the scramble to save people, bodies and the wounded were loaded onto handcarts and into pick-up trucks.

President Bush is to discuss the war in Iraq and the campaign against terrorism in a speech in Washington on Thursday.

On Wednesday, he met at the White House with senior Pentagon and military officials. One of those who briefed the president, Lt. Gen. David H. Petraeus, who just completed a tour as commander of the training program for Iraqi security forces, said later at the Pentagon that more than 36 Iraqi battalions were capable of leading combat operations, but with Americans alongside, supplying support and advice.

General Petraeus was trying to tamp down debate over statements by senior American commanders last week that only one Iraqi battalion was capable of conducting combat operations completely without American support, but he did not dispute that number.

Mr. Bush has offered no timetable for a possible reduction in American troops.

Abdul Razzaq al-Saiedi and Qais Mizher contributed reporting from Baghdad for this article, and Thom Shanker and Steven R. Weisman from Washington.