Baghdad, Iraq ? Nine U.S. soldiers were killed and 20 wounded Monday in a suicide car bombing against a patrol base northeast of the capital in Diyala province, a volatile area that has been the site of fierce fighting, the military said.

The attack came on a day when insurgents struck across Iraq, carrying out seven other bombings that killed at least 48 people.

Of the 20 wounded in the attack on Task Force Lightning in Diyala, 15 soldiers were treated and returned to duty while five others were evacuated to a medical facility for further care, the military said. An Iraqi civilian also was wounded.

Identities were not released pending notification of relatives.

It was the second bold attack against a U.S. base north of Baghdad in just more than 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, then 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.

Also Monday, U.S. officials 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 planned for Azamiyah 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 protested the wall.