Capping the bloodiest month for American troops since January, the U.S. military reported Monday that seven more U.S. service members were killed — all victims of increasingly sophisticated bombs that have been become the deadliest weapon in the insurgents' arsenal.

Bombs also claimed a toll Monday among civilians in Basra (search), Iraq's second-largest city and the major metropolis of the Shiite-dominated south, which has witnessed less violence than Sunni areas. A large car bomb exploded along a bustling street packed with shops and restaurants as people were enjoying an evening out after the daily Ramadan (search) fast. At least 20 were killed and about 40 wounded, police Lt. Col. Karim al-Zaidi said.

Military commanders have warned that Sunni insurgents will step up their attacks in the run-up to the Dec. 15 election, when Iraqis will choose their first full-term parliament since the collapse of Saddam Hussein's (search) regime in 2003.

To guard against such attacks, the military has raised the number of American troops in Iraq to 157,000 — among the highest levels of the Iraq conflict.

Most of the combat deaths and injuries in recent months have been a result of the increasing use by insurgents of sophisticated homemade bombs, responsible for the deaths of the seven Americans killed since Sunday. The military refers to those bombs as "improvised explosive devices," or IEDs.

Last Friday, an IED killed Col. William W. Wood (search), 44, of Panama City, Fla., an infantry battalion commander. He was promoted posthumously, making him the highest-ranking soldier killed in action in the Iraq conflict, according to the Pentagon.

"We see an adversary that continues to develop some sophistication on very deadly and increasingly precise stand-off type weapons — IEDs, in particular," Pentagon (search) spokesman Lawrence Di Rita told reporters Monday.

The insurgents continually search for new and more effective ways to use IEDs, di Rita said, while U.S. forces look for new ways to counter the threat.

"We're getting more intelligence that's allowing us to stop more of these things, find more of them. So we're learning from them and the enemy is learning from us, and it's going to be that way for as long as there is an insurgency," Di Rita said.

Monday's deadliest attack against U.S. service members came in an area known as the "triangle of death." Four soldiers from the U.S. Army's Task Force Baghdad (search) died when their patrol struck a roadside bomb in Youssifiyah, 12 miles south of Baghdad.

Two other soldiers from the Army's 29th Brigade Combat Team were also killed in a bombing Monday near Balad, 50 miles north of the capital. The U.S. military also reported that a Marine died the day before in a roadside bombing near Amiriyah, an insurgent hotspot 25 miles west of Baghdad.

The U.S. military death toll for October is now at least 92, the highest monthly total since January, when 106 American service members died — more than 30 of them in a helicopter crash that was ruled an accident. Only during two other months since the war began has the U.S. military seen a higher toll: in November 2004, when 137 Americans died, and in April 2004, when 135 died.

The latest deaths brought to 2,026 the number of U.S. service members who have died since the Iraq war began in March 2003. The number includes five military civilians.

The ongoing violence has killed a far greater number of Iraqis.

"They're obviously quite capable of killing large numbers of noncombatants indiscriminately, and we're seeing a lot of that, too," Di Rita said.

Public safety has deteriorated in recent months in Basra largely because of feuding among rival Shiite extremist groups that have infiltrated the police and security services. The city had previously been much more peaceful than Baghdad or cities within the volatile central, northern and western areas of the country where the Sunni Arab-led insurgency rages.

Earlier Monday near the Syrian border, Marines backed by jets attacked insurgent targets in a cluster of towns and villages near the Syrian border. The raid was part of an ongoing operation in an area believed heavily infiltrated by Al Qaeda (search) in Iraq and foreign fighters.

A Marine statement said U.S. aircraft fired precision weapons, destroying two safe houses believed used by Al Qaeda figures. The statement made no mention of casualties, but Associated Press Television News video from the scene showed residents wailing over the bodies of about six people, including at least three children.

At the local hospital, Dr. Ahmed al-Ani claimed 40 Iraqis, including 12 children, were killed in the attack. But the claim could not be independently verified, and figures from the area have sometimes proven exaggerated.

The footage from the scene showed Iraqi men digging through the rubble of several destroyed concrete buildings with a pitchfork or their hands. In the building of a nearby home, women wept over about half a dozen blanket-covered bodies lined up on a floor. Some of the blankets were opened for the camera showing a man and three children.

"At least 20 innocent people were killed by the U.S. warplanes. Why are the Americans killing families? Where are the insurgents?" one middle-aged man told APTN. "We don't see democracy. We just see destruction." He didn't give his name.