Gunmen armed with AK-47 assault rifles opened fire at an army checkpoint in the western Iraqi city of Fallujah on Saturday, killing four soldiers, according to a security official.

The attack in the center of the city followed an assault six days earlier in nearby Ramadi, when insurgents tried to blast their way into a police compound, setting off a deadly firefight with local police. After that attack, a police official warned that insurgents might soon target Fallujah.

On Saturday, about 7 p.m. local time, insurgents drove up to the Fallujah checkpoint in a four-wheel drive vehicle, said Lt. Col. Najim al-Dulaimi, a spokesman for Anbar province’s operations command.

Witnesses said the gunmen got out of their vehicle before opening fire. They shot two soldiers sitting in the back seat of a Humvee and two soldiers standing outside it, according to the witnesses. Dulaimi confirmed that four solders were killed.

The attack Saturday followed a wave of bombings over the past month, in the wake of the U.S. troop departure and amid a paralyzing political crisis. The major attacks began in Baghdad on Dec. 22 in various Shiite and Sunni neighborhoods and commercial areas. Then Shiite pilgrims were struck as they walked to religious shrines south of Baghdad. Ramadi and Fallujah, the sites of the latest attacks, are in the Sunni-dominated province of Anbar.

Officials in Iraq and Washington worry that insurgents are trying to provoke reactions from both Shiite and Sunni militias that could trigger bloody and disruptive sectarian battles across the country.

Also Saturday, an explosion occurred next to a military patrol just south of the city of Tikrit, injuring two soldiers, according to the al-Baghdadia TV channel’s news Web site. Farther north, in Kirkuk, gunmen killed a civilian and wounded a police officer, al-Baghdadia reported.

Special correspondents Uthman al-Mukhtar and Asaad Majeed contributed to this report.