Baghdad ? A suicide truck bomber flattened a Shiite mosque Friday in northern Iraq, and roadside bombs struck Shiite pilgrims in Baghdad, as at least 51 people were killed and scores wounded nationwide.

It was the second-deadliest day since U.S. forces turned over urban security to the Iraqis more than a month ago, raising fears that Sunni insurgents are intensifying a campaign to reignite sectarian violence that pushed the country to the brink of civil war.

The blast in a northern suburb of Mosul reduced the mosque and several nearby houses to rubble, leaving scores of worshippers and neighbors trapped underneath. Rescue crews and ordinary citizens joined forces to pull bodies from the debris and search for survivors.

At least 38 people were killed and some 200 wounded, according to police.