BAGHDAD — A roadside bomb killed four U.S. soldiers in Baghdad on Sunday, the military said, pushing the overall American death toll in the five-year war to at least 4,000.
The grim milestone came on the same day that rockets and mortars pounded Baghdad's U.S.-protected Green Zone and a suicide car bomber struck an Iraqi army post in the northern city of Mosul. The surge of attacks killed at least 66 other people nationwide.
The four U.S. soldiers were killed when a roadside bomb struck their patrol vehicle about 10 p.m. in southern Baghdad, according to a military statement. Identities of those killed were withheld pending notification of relatives.
Navy Lt. Patrick Evans, a military spokesman, expressed condolences to all the families who have lost a loved one in Iraq, saying each death is "equally tragic."
"There have been some significant gains. However, this enemy is resilient and will not give up, nor will we," he said. "There's still a lot of work to be done."
The 4,000 figure is according to an Associated Press count that includes eight civilians who worked for the Department of Defense.
Last year, the U.S. military deaths spiked along with the Pentagon's "surge" — the arrival of more than 30,000 extra troops trying to regain control of Baghdad and surrounding areas. The mission was generally considered a success, but the cost was evident as soldiers pushed into Sunni insurgent strongholds and challenged Shiite militias.
Military deaths rose above 100 for three consecutive months for the first time during the war: April 2007, 104; May, 126; and June, 101.
The death toll has seesawed since, with 2007 ending as the deadliest year for U.S. troops at 901 deaths. That was 51 more deaths than 2004, the second deadliest year for U.S. soldiers.
The milestones for each 1,000 deaths — while an arbitrary marker — serve to rivet attention on the war and have come during a range of pivotal moments.
When the 1,000th American died in September 2004, the insurgency was gaining steam. The 2,000-death mark came in October 2005 as Iraq voted on a constitution. The Pentagon announced its 3,000th loss on the last day of 2006 — a day after Saddam Hussein was hanged and the close of a year marked by rampant sectarian violence.
The deaths of U.S. soldiers in Iraq, however, are far less than in other modern American wars. In Vietnam, the United States lost, on average, about 4,850 soldiers a year from 1963 to 1975. In the Korean War, from 1950 to 1953, the United States lost about 12,300 soldiers a year.
But a hallmark of the Iraq war is the high wounded-to-killed ratio, partly because of advances in battlefield medicine, enhanced protective gear worn by soldiers and reinforced armored vehicles.
About 15 soldiers have been wounded for every fatality in Iraq, compared with 2.6 per death in Vietnam and 2.8 in Korea.
The deadliest month for American troops was November 2004, with 137 deaths. April 2004 was the next with 135 U.S. military deaths. May 2007 saw the third-highest toll.
December 2007 was the lowest monthly death toll, when 23 soldiers were killed — one fewer than in February 2004.
Two factors have helped bring down violence in recent months: a self-imposed cease-fire by a main Shiite militia and a grass roots Sunni revolt against extremists.
But commanders often say there is no guarantee the trends will continue. Sunday's violence that left more than 60 people dead underscored the fragile security situation and the resilience of both Sunni and Shiite extremist groups.
The deadliest attack was in Mosul, in northern Iraq, where a suicide driver slammed his vehicle through a checkpoint in a hail of gunfire and detonated his explosives in front of an Iraqi headquarters building, killing 13 Iraqi soldiers and injuring 42 other people, police said.
Iraqi guards opened fire on the vehicle but couldn't stop it because the windshield was bulletproof, an Iraqi army officer said.
In Baghdad, rockets and mortars began slamming into the Green Zone about sunrise, and scattered attacks persisted throughout the day.
At least five people were injured in the Green Zone, a U.S. Embassy statement said without specifying nationalities. A U.S. official said those injured included an American.
The zone includes the U.S. and British embassies as well as major Iraqi government offices.
No group claimed responsibility for the Green Zone attacks, but suspicion fell on Shiite extremists based on the areas from which the weapons were fired.