Four American soldiers were killed at a checkpoint in northern Iraq on Monday when a suicide car bomber attacked their vehicle, authorities said.

BAGHDAD — Four American soldiers were killed at a checkpoint in northern Iraq on Monday when a suicide car bomber attacked their vehicle, authorities said.

The U.S.-led Multi-National Force in Iraq said three soldiers died in the attack in the northern city of Mosul and a fourth later died of wounds. An interpreter also was killed, and two Iraqi police officers were wounded at the checkpoint.

Iraqi police said the suicide bomber attacked the American patrol in west Mosul around 12:40 p.m.

At least 4,243 members of the U.S. military have died in the Iraq war since it began in March 2003, according to an Associated Press count.

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The Pentagon said Monday’s attack was the deadliest since May 2, when four Marines were killed in a roadside bombing in Anbar province, once the heart of the Sunni insurgency.

The security situation in Iraq has improved significantly in recent months, with few American casualties. However, Monday’s attack highlights just how dangerous the country remains after almost six years of sectarian bloodshed.

Despite the security clampdown, Mosul remains something of a battleground where relations are uneasy between Arabs and Kurds.

Tensions ran especially high on Jan. 31, when Iraq held provincial elections for 14 of its 18 provinces. In Nineveh, where Mosul is, the Kurdish parties in power were defeated by the Sunni Arab nationalist party al-Hadbaa, which garnered 48.8 percent of the vote.

Monday was a violent day in Mosul. Two children were wounded in a roadside bombing, and a mortar attack killed three people, two of them police officers. Seven others, including a police officer, were wounded.

In Baghdad, a mortar attack Monday evening wounded seven.