BAGHDAD (AP) — Three car bombs ripped through an outdoor market in Mosul on Thursday, killing at least 15 civilians and eight policemen, the Iraqi Defense Ministry said in a statement.

The attack occurred in the eastern district of Gogjali, which Iraqi forces retook from Islamic State militants weeks ago as part of a massive operation to drive them from Mosul, the brief statement said. It did not say whether the explosions were caused by suicide attackers.

Earlier Thursday, the United Nations denounced the killing of four aid workers and seven other civilians in two mortar attacks in Mosul this week. The U.N. mission said the attacks occurred on Tuesday and Wednesday in eastern Mosul, and wounded up to 40 others. The U.N. did not identify the aid workers or provide their nationalities.

On Wednesday, Human Rights Watch said Islamic State fighters are deliberately targeting civilians in areas they have lost to government forces. The New York-based group said that Mosul civilians were increasingly being caught in the crossfire, with at least 19 killed and dozens wounded in the period from the third week of November into the first week of December.

Backed by the U.S.-led international coalition and paramilitary forces, the Iraqi military launched a campaign in October to retake Mosul, the country's second largest city and the last major IS urban bastion in Iraq. The troops' advances slowed once they pushed into more densely populated areas.

IS captured Mosul in the summer of 2014 as part of a blitz that placed nearly a third of Iraq under their control. Since last year, IS has lost large swaths of territory in western and northern Iraq.