Shiite militiamen loyal to a fiery anti-American Shiite cleric re-emerged in the troubled southern city of Amarah on Monday, dragging four policemen aligned with a rival Shiite militia from their homes and killing them.

Witnesses said the Iraqi army, camped on the edge of the city, was doing nothing to stop the resurgence of Shiite-on-Shiite violence. Iraq's leaders sent a force of about 500 soldiers to the city late last week after Muqtada al-Sadr's Mahdi Army militiamen stormed the city and attacked police stations, manned primarily by loyalists of the rival Badr Brigades, also a Shiite militia.

At least 25 fighters and police died in those gunbattles before politicians intervened and won a promise from the Mahdi Army gunmen to leave the streets. In the meantime, virtually all of the Amarah police force went into hiding.

The renewed unrest in Amarah came as the U.S. military reported that a Marine had died in fighting in the restive western province of Anbar on Saturday, bringing the number of U.S. troops killed in October to 86 -- the highest monthly toll since November 2004.

The Iraqi prime minister, meanwhile, warned the country against lawlessness and said his military would take unspecified action to stop the mounting bloodshed.

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"Let everyone be informed that orders have been issued to the armed forces to stop any transgression against state power and to confront any illegal attempt regardless of its source," Nouri al-Maliki said in a statement.

"The Iraqi government also calls in particular on the people of Maysan province (home to Amarah) to exercise caution and care in the face of attempts to drag the people of this unified nation into fighting and strife," the Shiite prime minister said.

Al-Maliki has faced growing pressure from allies in Washington and London to rein in Shiite militias and other violent factions, and his Monday statement appeared to be a reaction.

The White House said Monday that the fledgling Iraqi government must step up and take more responsibility for the country's security.

But President Bush's spokesman, Tony Snow, discounted a newspaper report saying the head of the U.S.-led Multinational Forces in Iraq and the U.S. ambassador were working on a plan that -- for the first time -- would set a specific timetable for disarming militias and meeting other political and economic goals.

"There is still a very large to-do list before Iraq is in a position to sustain, government and defend itself," Snow said.

"Are we issuing ultimatums? No," he added.

But with the army apparently on the sidelines and unwilling to stop the bloodshed in Amarah, 200 miles southeast of Baghdad, it was unclear what effect the statement would have there or elsewhere in the country.

In Amarah, gunmen dragged police Lt. Sarmad Majid al-Shatti from his home before dawn, then dumped his bullet-riddled body at a farm on the city's outskirts, said Ali Chaloub of Sadr General Hospital. Another policeman, Lt. Alaa al-Kabi was shot to death outside his home, Chaloub said.

At about the same time, provincial policemen Hamid Majeed and Hassan Abdullah were kidnapped from their homes, and their bodies were later found dumped outside the city, Chaloub said.

Badr fighters took revenge, killing and beheading the teenage brother of the local Mahdi Army commander. The Mahdi commander was killed Thursday, setting in motion the Amarah violence.

With sectarian violence between Sunnis and Shiites also on the rise, Sunnis in Baghdad largely ignored public celebrations of the Eid al-Fitr feast marking the end of the Ramadan month of fasting. They said they feared new attacks.

In Baghdad Monday, a car bomb killed at least three people. Police said the explosion on Palestine street had targeted a police patrol, but it's victims, including 13 injured, were merely pedestrians, police Lt. Thair Mahmod said.

U.S. commanders and Iraqi officials have hoped for a reduction of violence after Ramadan.

According to an Associated Press count, October is on track to be the deadliest month for Iraqis since the AP began tracking deaths in April 2005. Through Sunday, October 22, at least 941 Iraqis have been killed in war-related violence, an average of 43 every day.

That compares to an average daily death toll of about 27 since April 2005. The AP count includes civilians, government officials and police and security forces, and is considered a minimum based on AP reporting. The actual number is likely higher, as many killings go unreported.

Despite the worsening carnage, Iraqi Deputy Prime Minister Barham Saleh said on a visit to Britain that international forces must not abandon Iraq while the situation there remains volatile.

"I do believe there is no option for the international community to cut and run," Saleh told reporters after meeting British Prime Minister Tony Blair in London. About 7,000 British troops are assigned to southern Iraq as part of the U.S.-led coalition force in the country.

Saleh said Iraqi forces will be in control of seven or eight of Iraq's 18 provinces by the end of the year, adding: "We understand that this cannot be an open-ended commitment by the international community."

The near absence of public displays of jubilation in Baghdad's Sunni areas reflects the worsening security in the capital, whose 6 million residents are about evenly divided between Shiites and Sunnis, making it the main battlefield in the country's widening sectarian violence.

Iraq's majority Shiites will celebrate the three-day Eid al-Fitr Tuesday or Wednesday, which means Monday to them could be the last day of the fast when devout Muslims refrain from food, water, sex and smoking from dawn to dusk.

Despite an increased police and army presence on the streets, many Baghdad Sunnis said they would rather stay home than risk falling victim to car bombs or Shiite death squads.

"We are telephoning friends and relatives or sending text messages to wish them a happy holiday," said Nadhim Aziz, a math teacher from the city's mixed district of New Baghdad.

He said he found fewer worshippers than last year when he went to a local mosque to perform the early morning prayers marking Eid al-Fitr.

"We were 50 to 60 in the mosque. Last year, there were about 400," Aziz lamented.

Complete coverage is available in FOXNews.com's Iraq Center.