American forces are facing an increasingly dangerous environment in southern Iraq, where Shiite militias trying to claim they are driving out the U.S. occupiers have stepped up attacks against bases and troops.
The uptick in violence serves as a warning about what American forces could face if U.S. and Iraqi officials come to an agreement about keeping more U.S. troops in the country past Dec. 31.
"We're very concerned about it," said Col. Reginald Allen, who commands the 3rd Armored Cavalry Regiment that operates in five, predominantly Shiite provinces. "This environment is very fluid, but in general our planning assumptions and our precautions are based on the worst case, that levels of violence will continue to increase."
Allen's regiment lost five soldiers in April, one of the highest months for combat-related deaths in Iraq since U.S. forces pulled out of the cities in June 2009.
Two were killed in Babil province by indirect fire _ the military's term for rockets or mortars; two more were killed by a roadside bomb in Wasit province, which borders Iran; and the last was killed by a rocket-propelled grenade in Qadisiyah province.
About 46,000 American troops remain in Iraq, focusing on training Iraqi forces. That's down from their one-time high in 2007 of nearly 170,000 troops. U.S. soldiers still come under attack from rockets or mortars on their bases, and from roadside bombs and shootings when they're moving around the country.
Michael Knights, of the Washington Institute for Near East Policy, said the attacks indicate an increased confidence by militias to engage U.S. forces. He noted that the militants have been targeting vulnerable U.S. supply lines. The vast majority of supplies for U.S. forces are shuttled on roads from Kuwait into southern Iraq.
Knights, who writes extensively about security issues in Iraq, said April saw a major jump in the use of armor-piercing explosives _ known as explosively formed penetrators, or EFPs.
"The increase in attacks shows that Iranian-backed cells enjoy greater freedom of movement than they have in the past. They have increased confidence in their ability to engage U.S. forces in stand-up firefights in broad daylight," he said.
American forces in Iraq have always faced a two-pronged threat: Sunni-led insurgents like al-Qaida in Iraq and Shiite militias with ties to Iran.
The Sunni-led insurgents have tended to operate in the western Anbar province, northern areas like Mosul and in Baghdad and its suburbs, while Shiite militias have generally battled American troops in and around Baghdad and in southern Iraq, where Shiites dominate.
The Shiite militias in the south have recently been causing the most problems for American forces.
"If you look into the south, what we see, it's very, very problematic," said Lt. Gen. Frank Helmick, second-in-command of U.S. forces in Iraq.
"You can see an uptick in indirect fire activity down in the south _ in other words, rockets and mortars and there's been an IED threat that is becoming more problematic than in the past down in the south. So we see a lot of activity," he said.
The militants' goal is simple, say U.S. officials. By attacking U.S. forces, who are scheduled to leave by the end of this year, they are trying to portray themselves as driving out the Americans.
By laying claim to being the true voice of resistance to the "occupiers," they hope to rally support among the mostly poor Shiite population in the south and gain influence after the American military goes home. Since the war began in 2003, 4,452 American military personnel have died in Iraq, according to an Associated Press count.
In one recent statement on a militant website, a group called Kataib Hezbollah said its attacks were aimed at stopping the "occupation interference" in Iraq's affairs and forcing the U.S. to abide by the withdrawal deadline.
There are a combination of Shiite militias operating in southern Iraq, each claiming credit for various attacks, Helmick and Allen said.
The groups include Kataib Hezbollah, which has links to the Lebanon-based Hezbollah group; League of the Righteous, also known by its Arabic name, Asaib Ahl al-Haq; and the Promised Day Brigade, affiliated with anti-American cleric Muqtada al-Sadr. All are believed to get financing and support from Iran, according to a recent report from the Washington Institute for Near East Policy.
U.S. officials have long contended that Shiite militias operate with funding and weapons funneled in from Iran, a charge Iran denies.
The weapons go from the Diyala River Valley along the Iranian border northeast of Baghdad to the southern Iraqi port of Umm Qasr on the Persian Gulf, said a U.S. military official speaking on condition of anonymity to discuss sensitive information.
Buses carrying Iranian religious pilgrims into Iraq are possibly used to smuggle weapons as well, the official said.
Under a 2008 agreement, all American forces are to leave Iraq by the end of the year. The U.S. has said it is open to keeping more troops here beyond the deadline but only if Iraq asks. Prime Minister Nouri al-Maliki has said he is going to meet with all factions this month to discuss the issue.
Iranian opposition to any extended American troop presence in Iraq could translate into more attacks against U.S. forces. Already al-Sadr has threatened violence if American troops stay into 2012.
"Though effective attacks are still rare the deaths of five U.S. troops in one month is a warning that more determined Iranian-backed attacks could continue if the United States pushes its present initiative to keep a residual force in Iraq," Knights said.
Associated Press writer Lara Jakes in Baghdad contributed to this report.