BAGHDAD – Suicide attackers struck near a Shiite mosque north of Baghdad and a checkpoint west of the capital Monday as bombings killed at least 17 people nationwide.

The violence was concentrated in former Sunni insurgent strongholds that have seen a sharp decline in violence after local tribal leaders turned against al-Qaida in Iraq. Despite the relative calm, a series of deadly bombings have raised concerns about a resurgence of violence as the U.S. military scales back its presence, with a full withdrawal planned by the end of 2011.

The attacks – which mainly targeted checkpoints and Iraqi policemen – also highlighted the weaknesses in the Iraqi security forces, which are struggling to prove they are ready to take over from the Americans.

The deadliest attack was a suicide car bomber who struck a line of vehicles waiting to be inspected before crossing a bridge near the Anbar provincial capital of Ramadi, police said.

The blast set half a dozen other vehicles ablaze, killing three policemen and five civilians and wounding 16 other people, according to police and hospital officials, who spoke on condition of anonymity because they were not allowed to release the information.

A farmer riding in a pickup truck not far behind the attacker’s car ran toward the scene, where he described seeing a child who had been blown by the blast onto the roof of a car.

“I tried to approach him to see whether he was alive or dead, but the police started to open fire in all directions and we had to run away,” he said. Iraqi police frequently fire into the air at bombing sites to disperse the crowd and scare away other potential attackers.

Ramadi, 70 miles west of Baghdad, was once one of the most dangerous cities in Iraq before the U.S.-funded Sunni revolt against al-Qaida more than two years ago.

Hours later, a suicide bomber wearing a police uniform blew himself up at the gate of a Shiite mosque in Baqouba, 35 miles northeast of Baghdad, killing at least five people – three policemen and two worshippers – and wounding 20, according to police and hospital officials.

Maj. Ghalib al-Karkhi of the provincial police said the bomber was forced to detonate his explosives prematurely after guards stopped him and asked for his ID card.

The mainly Sunni city of Baqouba also has been hit by several bombings despite an overall decline in violence.

In Baghdad on Monday, a bomb destroyed a police car, killing one officer and two civilians and wounding eight, police said. Another bomb killed a driver as he approached a military checkpoint in the Sadr City district.