Updated

U.S. and Iraqi forces fighting insurgents near the Syrian border ran into fierce resistance Tuesday, with troops encountering dozens of explosive booby traps and killing at least 30 insurgents, the military said.

The U.S. command said three U.S. Marines have died in combat while trying to clear the town of Obeidi as part of "Operation Steel Curtain" since Monday. At least 80 insurgents have been killed in the same period, mostly in airstrikes, the statement said.

"Iraqi and coalition forces continue to clear the city house by house, occasionally encountering buildings that are rigged with explosives and triggered to detonate upon entering the building," the statement said.

"Numerous weapons caches have also been seized, to include several that contained suicide vests and bomb-making material."

The U.S.-Iraqi attack on Obeidi was the latest stage of an offensive to clear Al Qaeda-led insurgents from a string of towns and cities in the Euphrates River valley near the border with Syria and seal off a major route for foreign fighters sneaking into Iraq.

"Intelligence reports indicate that the strong resistance to the Iraqi and coalition push into the city is due in large part to the fact that insurgents believe they are trapped and have nowhere else to go," the military said. "Several detainees were captured trying to sneak out of the area by crawling among a flock of sheep."

Earlier this month, U.S. and Iraqi forces overran two other towns in the area, Husaybah and Karabilah. Unlike previous sweeps in the area, the Americans and their Iraqi allies plan to establish a long-term presence to keep insurgents from returning.

U.S. officials have said the Euphrates Valley campaign is also aimed at encouraging Sunni Arabs there to vote in the Dec. 15 parliamentary elections without fear of insurgent reprisals. The Bush administration hopes a successful election with strong Sunni Arab participation will encourage many in that community to abandon the insurgency.

One Marine died Tuesday from wounds incurred from a bomb that exploded day before, the military said. The other two Marines were killed Monday — one by a roadside bomb in Obeidi, and the other by small arms fire, it said. All were assigned to Regimental Combat Team 2, 2nd Marine Division.

The deaths brought to 2,071 the number of U.S. service members who have been killed since the war started in 2003, according to an Associated Press count.

Prime Minister Ibrahim al-Jaafari confirmed Tuesday that more than 173 Interior Ministry prisoners were found malnourished and possibly tortured by the new government's security forces.

Al-Jaafari's comments came a day after an Interior Ministry official said an investigation will be opened into allegations that its officers tortured suspects detained in connection with Iraq's insurgency.

"I was informed that there were 173 detainees held at an Interior Ministry prison and they appear to be malnourished. There is also some talk that they were subjected to some kind of torture," al-Jaafari said at a news conference.

Maj. Gen. Hussein Kamal, the Interior Ministry's undersecretary for security, said the detention center was in Baghdad.

Late Sunday, U.S. troops surrounded and took control of an Interior Ministry building in Baghdad, apparently in connection with repeated allegations that Iraq security forces were illegally detaining and torturing people suspected of taking part in the insurgency.

In attacks aimed at Iraqi police Tuesday, insurgents opened fire on a police patrol in Kirkuk, 180 miles north of Baghdad, killing four, while a roadside bomb a few miles away killed two more police officers, Col. Shirzad Mursi said. The son of an Iraqi contractor was also killed, he added.

In Baghdad, a car bomb exploded while a group of police gathered for a meeting, police Capt. Haider Ibrahim said. Four people were killed, including two officers, and seven people were wounded, he said.

Major Sunni Arab politicians and religious leaders complained Monday that military activities like Operation Steel Curtain will discourage voter turnout in predominantly Sunni areas. Iraq's Sunni vice president also has called for halting such operations, especially in western Iraq and in a province around the city of Baqouba.

"These military operations have gone too far and have a negative impact on the country's politics," Vice President Ghazi al-Yawer told Al-Arabiya television.

Hundreds of Sunni Arabs marched Monday through the streets of Baqouba, 35 miles northeast of Baghdad, to protest Iraqi security raids in the surrounding province over the weekend. More than 300 people, mostly Sunni Arabs, were arrested, officials said.

Members of the crowd carried banners denouncing the arrests of Sunni Arabs and chanted, "No to America, no to Britain!"

Most Sunni Arabs boycotted the Jan. 30 elections, enabling the majority Shiites and their Kurdish allies to dominate the current parliament. Many Sunni politicians now consider the boycott a mistake and have urged fellow Sunnis to vote next month, although hard-liners in the insurgency and among the Sunni clergy remain opposed.

With casualties rising and elections just a month away, U.S. and other countries have stepped up diplomatic efforts to try to reconcile Iraq's disparate factions. Secretary of State Condoleezza Rice, British Foreign Secretary Jack Straw, U.N. Secretary-General Kofi Annan and former Russian Foreign Minister Igor Ivanov have all visit Baghdad in the past five days to encourage successful elections.

Arab League officials said 100 prominent Iraqis have been invited to a weekend meeting in Egypt to pave the way for a full-blown conference, probably to be held early next year in Iraq. The preliminary meeting is not expected to include representatives of insurgent groups or Saddam Hussein loyalists.