Insurgents stepped up attacks on Iraq's fledgling security forces, killing seven Iraqi police and guardsmen Monday in a suicide bombing hours after storming a police station north of the capital. The military reported five new U.S. deaths.

Thirteen Marines were wounded Monday in a mortar attack south of Baghdad, the military said. No further details were released.

Military offensives in Fallujah (search) and elsewhere have made November the second deadliest month for U.S. troops since the March 2003 invasion, with at least 133 American dead.

Monday's suicide attack occurred in Baghdadi a Euphrates River town about 120 miles northwest of the capital, where a driver detonated his vehicle near a police checkpoint, police Lt. Mohammed al-Fehdawi said. A hospital official, Hatim Ahmed, confirmed seven police and Iraqi National Guard members were killed and nine were wounded.

Late Sunday, gunmen stormed a police station west of Samarra (search), 60 miles north of Baghdad, looted the armory, commandeered several police cars and fled after encountering no resistance, Iraqi officials said.

U.S. troops went to the police station Monday morning and arrested two dozen people, police said. American officials had no comment. U.S. and Iraqi troops recaptured Samarra from insurgents in September, but the city remains tense.

Two American soldiers from Task Force Baghdad were killed and three wounded Monday in a roadside bomb explosion in northwestern Baghdad, the U.S. command said. One American soldier died and two were injured in a vehicle accident 30 miles northwest of the town of Kut in eastern Iraq, the military said.

In addition, two U.S. Marines were killed in a weekend bombing south of the capital, a U.S. official said Monday. U.S., British and Iraqi forces have been sweeping through the area to clear Sunni insurgents from a string of towns and cities between Baghdad and the Shiite shrine cities of Najaf and Karbala.

Attacks have increased against U.S., Iraqi and other targets on the road leading from the center of Baghdad to the city's international airport, located on the western outskirts of the capital.

The British Embassy announced Monday that its staff would no longer be permitted to travel on the airport road, which the U.S. State Department has identified as one of the most dangerous routes in Iraq.

"We advise against all but essential travel to Iraq," the British Embassy said in a statement. "We urge all British nationals in Iraq to consider whether their presence in Iraq is essential at this time. Even essential travel to Iraq should be delayed, if possible."

South of the capital, U.S., British and Iraqi forces pressed an offensive aimed at clearing insurgents from an area known as the "triangle of death." Two Marines were killed there Sunday, U.S. officials said, and British troops escaped serious injury Monday when a bomb exploded next to a Scimitar light tank from the Queen's Dragoon Guards.

The offensive, called Operation Plymouth Rock, was launched in part as a follow-up to this month's assault on Fallujah, the main insurgent bastion 40 miles west of Baghdad.

U.S. commanders want to cut off an escape route for Fallujah fighters and pacify the area so that national elections can be held Jan. 30. Sunni Muslim clerics have called for an election boycott, and leading Sunni politicians urged the vote be postponed. Leaders from the majority Shiite community have demanded the elections go ahead as scheduled.

In Mosul, however, the top U.S. commander told the British Broadcasting Corp. that elections could not be held in all parts of the city, Iraq's third largest, under current security conditions. But Brig. Gen. Carter Ham said there was still time to get the situation under control.

The Pentagon, meanwhile, said Monday the U.S. military death toll in Iraq since the U.S.-led invasion in March 2003 stands at 1,251. That is up 21 since the Pentagon last reported a total on Nov. 24. At least 133 American troops have died in Iraq this month, including the two killed in Baghdad and a third who died in a vehicle accident in east-central Iraq on Monday. The deadliest month for U.S. troops in Iraq was last April, when 135 died.

In Geneva, the international Red Cross said Iraq's Red Crescent had set up a relief center in Fallujah to aid civilians, but doctors and nurses have been unable to treat the wounded because of continued fighting between U.S.-led forces and insurgents.

"There are many civilians who are still trapped in the city and don't dare to come to the Red Crescent office," said Rana Sidani of the International Committee of the Red Cross.

She said there was a shortage of drinking water in Fallujah and the city water purification station was not working "because there is nonstop fighting around it."

At the Pentagon, spokesman Bryan Whitman said American troops in Fallujah reported finding nearly as many homemade explosives over the past three weeks as had been uncovered throughout Iraq in the previous four months.

Whitman said that in the Fallujah operations, troops found at least 650 homemade bombs, compared with 722 found throughout the country between July 1 and October 31.

The attacks against Iraqi forces have raised concern, not only because of the many casualties but because most of the units have not been combat-tested. U.S. officials hope to transfer more security responsibility to the Iraqis, enabling the American military to draw down from the more than 138,000 troops now in the country.

The governor of Iraq's Shiite-dominated Najaf province said police had arrested his own security chief after uncovering an alleged plot to assassinate top regional officials -- including himself. The aide, Ali al-Sheibani, was detained late Sunday, Gov. Adnan al-Zurufi told reporters on Monday.

"Ali al-Sheibani was arrested because he was planning to establish a terrorist cell aiming at assassinating the governor and other officials in Najaf," he said.

Although some Iraqi units are said to have performed well in Fallujah and other operations, others have not. The entire 5,000-member police force in the northern city of Mosul disintegrated during an insurgent uprising this month, forcing the government to send in reinforcements.

At least 50 people have been killed in Mosul in the past 10 days -- most of them believed to have been supporters of Iraq's interim government or members of its security forces.

A statement posted on an Islamic Web site in the name of Al Qaeda in Iraq, led by Jordanian terrorist Abu Musab al-Zarqawi, claimed responsibility for killing 17 security force members and a Kurdish militiaman in Mosul. The claim could not be authenticated.