An Iraqi civilian also was wounded in the attack on Task Force Lightning soldiers in Diyala province, a volatile area that has been the site of fierce fighting involving U.S. and Iraqi troops, Sunni insurgents and Shiite militias.
At least 48 Iraqis were killed in seven other bombings, violence that has persisted despite a nearly 10-week-old U.S.-Iraqi security crackdown aimed at pacifying Baghdad.
Of the 20 wounded in the attack on the patrol base, 15 soldiers were treated and returned to duty while five others and the Iraqi were evacuated to a medical facility for further care, the military said.
Identities were not released pending notification of relatives.
It was the second bold attack against a U.S. base north of Baghdad in just over two months and was notable for its use of a suicide car bomber.
On Feb. 19, insurgents struck a U.S. combat post in Tarmiyah, about 30 miles north of Baghdad, killing two soldiers and wounding 17 in what the military called a "coordinated attack." It began with a suicide car bombing followed by gunfire on soldiers pinned down in a former Iraqi police station where fuel storage tanks were set ablaze by the blast.
Militants have mostly used hit- and-run ambushes, roadside bombs or mortars on U.S. troops and stayed away from direct assaults on fortified military compounds to avoid U.S. firepower.
American troops are facing increasing danger as they step up their presence in the Baghdad area as part of the security crackdown to which President Bush has committed an extra 30,000 troops.
Sunni militants are believed to have withdrawn to surrounding areas such as Diyala province where they have safe haven. The U.S. command also deployed an extra 700 soldiers to the area last month.
The deaths raised to 85 the number of U.S. service members who died have in Iraq in April, making it the deadliest month for American troops since December, when 112 died.
It was the single deadliest attack since Dec. 1, 2005, when a roadside bomb killed 10 Marines and wounded 11 on a foot patrol near Fallujah.
Twelve soldiers died when a Black Hawk helicopter crashed in Diyala on Jan. 20. The military said it might have been shot down but the investigation is still ongoing. A U.S. soldier also was killed Monday in a roadside bombing in Muqdadiyah, about 60 miles north of Baghdad, the military said in an earlier statement. A British soldier was shot to death while on patrol in the southern city of Basra, officials said.
A suicide car bombing also struck a police station in the Diyala provincial capital of Baqouba, killing 10 people.
U.S. officials, meanwhile, signaled that they might reconsider putting a three-mile concrete barrier around a Sunni Arab neighborhood in Baghdad after Iraq's struggling prime minister came under pressure from Sunnis and ordered the project halted.
Plans for the separation barrier to protect the Azamiyah neighborhood were in doubt after Prime Minister Nouri al-Maliki criticized the idea of creating "gated communities" to separate Baghdad's sectarian neighborhoods. Speaking during a tour of Sunni-led Arab countries, the Shiite Muslim prime minister said he did not want the 12-foot-high wall to be seen as dividing the capital's sects. Iraq's Sunni Arab minority dominated during Saddam Hussein's reign, and its members remain deeply distrustful of Shiite intentions and provide the backbone of the Iraqi insurgency. Shiite militias, in turn, have been attacking Sunni neighborhoods in retaliation for insurgent attacks on their own communities. Azamiyah's Sunni residents have been the target of frequent mortar attacks by Shiite militants, but hundreds of people in the district took to the streets to protest against the wall, saying it would make their neighborhood "a big prison." The new American ambassador to Iraq, Ryan Crocker, defended the barrier plan Monday, saying it was an effort to protect the Sunni community from surrounding Shiite areas, not to segregate it. Holding his first news conference since taking his post, Crocker said security measures were implemented in coordination with the Iraqi government. "Obviously, we will respect the wishes of the government and the prime minister," he said, although he did not say construction would halt. Al-Maliki said he would not allow "a separation wall," but then he said that the subject would be discussed and that he would not rule out all barriers, such as barbed wire. Iraq's chief military spokesman indicated that some type of barrier would go up, saying al-Maliki was responding to exaggerated reports about the wall. "We will continue to construct the security barriers in the Azamiyah neighborhood. This is a technical issue," Brig. Gen. Qassim al-Moussawi said at a joint news conference with a U.S. military spokesman, Rear Adm. Mark Fox. "Setting up barriers is one thing and building barriers is another. These are moveable barriers that can be removed." Al-Moussawi noted that similar walls made of sections of concrete are in place elsewhere in Baghdad, including in other residential neighborhoods. The confusion over the barrier reflected a lack of coordination between al-Maliki's government and the U.S. military even as they have touted their partnership the nearly 10-week-old security operation in Baghdad. Lt. Col. Christopher Garver, a U.S. military spokesman, said there may have been miscommunication. "Discussions on a local level may not have been conveyed to the highest levels of the Iraqi government," Garver said. "Whether the prime minister saw this plan or not, I don't know. With him in Cairo, it complicates things." Al-Maliki's comments came as he faces heavy pressure to bring Sunnis into the political process and dampen support for the insurgency amid unrelenting violence despite the crackdown in the capital. He had assured Washington that he would not allow political considerations to influence tactical decisions, but his criticism of the wall followed a wave of outrage from Azamiyah's residents and Sunni leaders after the U.S. military announced its plan last week. Protesters in Azamiyah carried banners Monday with slogans such as "No to the sectarian wall" and "Azamiyah children want to see Baghdad without walls" as they marched from a mosque to a former police station that now houses an outpost of U.S. soldiers. "The real reason behind this wall is to increase peoples' sufferings and complicate their daily lives," said one protester, engineer Khalil al-Obaidi. Sheikh Sameer al-Sumaidaie, a preacher at the mosque where the protest started, said: "We had a united country before the war, but now it is being divided into fragments." Al-Maliki has thwarted U.S. plans in the past. In October, U.S. troops pulled down roadblocks around Baghdad's Shiite slum of Sadr City on his order. At the time, the prime minister was said to have feared violence from the Mahdi Army, the Shiite militia that is headquartered in Sadr City and loyal to the anti-American cleric Muqtada al-Sadr. Al-Maliki is under intense pressure from the Bush administration to show progress with security and national reconciliation efforts as the war grows increasingly unpopular in the United States. In Washington, Senate Majority Leader Harry Reid said Congress would ignore a presidential veto threat and pass legislation within days requiring the withdrawal of U.S. combat troops from Iraq beginning Oct. 1, with a goal of completing a full pullout in six months. Bush promised to reject any legislation setting a schedule for leaving Iraq. AP-CS-04-23-07 2306EDT