Iraqi Officials Say 13 Dead in Wave of Bomb Blasts A series of morning bomb explosions in Baghdad and the northern Iraqi city of Mosul on Thursday killed at least 13 people and wounded dozens in the latest eruption of violence rattling the country, officials said. Iraq is facing its most relentless wave of violence since the 2011 U.S. military withdrawal, deepening fears that the country is heading back toward the widespread sectarian fighting that pushed it to the brink of civil war in the years after the invasion. More than 500 people have been killed in May. The extent of the bloodshed is increasingly reminiscent of the widespread sectarian fighting that peaked in 2006 and 2007 and threatened to tear the country apart. Most of Thursday's blasts went off in Baghdad. Car bombs killed four in the northeastern Shiite neighborhood of Binouq, and three died in a bombing at a market selling spare car parts in central Baghdad, according to police. Police officials also said that a roadside bomb exploded on a police patrol in the largely Shiite central commercial district of Karradah, killing three people there. In the northern city of Mosul, two police officers said a suicide bomber killed three when he blew himself up on a federal police checkpoint. Mosul is a former insurgent stronghold, located about 360 kilometers (225 miles) northwest of Baghdad. All officials spoke on condition of anonymity because they weren't authorized to talk to the media. There was no immediate claim of responsibility for the attacks but blame is likely to fall on al-Qaida's Iraq arm, which frequently carries out bombing attacks against civilians and security forces in an effort to undermine faith in the Shiite-led government. Other militant groups have also grown more active in recent months, including the Army of the Men of the Naqshabandi Order, which has ties to members of Saddam Hussein's now-outlawed Baath party. The attacks came hours after bomb blasts tore through two Baghdad neighborhoods Wednesday evening. At least 30 people were killed, including several members of a wedding party in the mixed Sunni-Shiite Jihad neighborhood. The southwestern neighborhood was one of the earliest flashpoints in Baghdad's descent into sectarian bloodshed in the years following the 2003 U.S. led invasion. It housed mainly Sunni civil servants and security officials under Saddam Hussein's regime, though many Shiites now live there too. Many of Jihad's Sunni residents earlier this year received threatening leaflets from a Shiite militant group, the Mukhtar Army, warning them to leave. Associated Press writer Adam Schreck contributed to this story .