BAGHDAD , Iraq ( CNN ) -- Six car bombings in four hours killed 48 people and wounded 81 in various Baghdad neighborhoods Wednesday , according to Iraq 's Interior Ministry . Iraqi soldiers survey one of the Baghdad marketplaces where car bombs detonated Wednesday . In a separate incident , five people were killed and three wounded by a roadside bomb south of Baghdad , a ministry official said . Most of the deaths came when three car bombs parked at separate but nearby marketplaces exploded in quick succession in the eastern Baghdad Shiite neighborhood of Sadr City , killing at least 45 people and injuring at least 68 , the ministry official said . Three other car bombings followed . Two of those , outside a Shiite mosque in the Hurriya district of northern Baghdad , killed three people and wounded eight . The bombs exploded in close succession shortly before 9 p.m. ( 2 p.m . ET ) . A third a few hours earlier injured at least five civilians in a predominantly Shiite area of southwestern Baghdad , according to the ministry . Wednesday 's series of bombings echoed an incident earlier this month , when seven car bombs detonated within about four hours . The U.S. military blamed al Qaeda in Iraq for what it called coordinated attacks . Sadr City is a heavily populated Shiite area , with an estimated 2.5 million people packed into a 25-square-kilometer area . The district was a stronghold of Shiite cleric Muqtada al-Sadr 's Mehdi Army , but most of the fighters went underground after fierce fighting in April 2008 . In a seventh bombing Wednesday night , at least five people died and three were wounded south of Baghdad , a ministry official said . A roadside bomb struck a minibus in Hor Rajab , a predominantly Sunni area on the southern outskirts of Baghdad . The casualties were all civilians , the official said . There has been an uptick in bombings and attacks in recent weeks , mainly targeting Shiites and Shiite areas . Last Thursday and Friday , five suicide bombings , as well as other attacks in Baghdad and Diyala province , left almost 160 people dead and 275 wounded . Earlier Wednesday , U.S. and Iraqi troops were ambushed in northern Iraq , according to Maj. Derrick Cheng , spokesman for the U.S. military 's Multi-National Division-North . The troops were on a joint mission in Riyadh , southwest of Kirkuk , where coalition forces are working with local police to provide micro-grants to small businesses , Cheng said . Several individuals attacked the troops using at least one grenade and small arms fire , he said . Cheng said two of the attackers reportedly were killed and another two were wounded . A woman reportedly was injured by shrapnel from the grenade , but was treated and released , he said . A soldier was reported wounded but was in good condition , Cheng said . So far this month , 15 U.S. soldiers have died in Iraq , compared to nine in March -- most of those in non-combat-related incidents . March 's death toll was the lowest monthly toll for the U.S. military since the war began 2003 . The Riyadh incident comes at a time of heightened tension between the U.S. military and the Iraqi government , after two Iraqis were killed during a military raid south of Baghdad on Sunday . Iraqi state TV reported that Iraqi Prime Minister Nuri al-Maliki accused U.S. troops of violating the security agreement between the two countries with the raid in Wasit province . CNN 's Jomana Karadsheh contributed to this report .
Six car bombs explode in Baghdad , Iraq 's Interior Ministry says . Separate roadside bombing south of Baghdad kills five civilians , official says . U.S. , Iraqi troops ambushed in northern Iraq ; two attackers killed , U.S. military says .