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Khalid Mohammed, Associated Press
Mourners pray over the body of Musaap Yaser Hazem, 17, who died in a Islamic State mortar attack, during his funeral, in Mosul, Iraq, Wednesday, Jan. 11, 2017. Hazem's father said his son was killed during a Islamic State mortar attack in early December 2016, and had to be buried in the neighborhood because of the poor security situation. On Wednesday, approximately a month after he died, the security situation had improved and the family were finally able to give Hazem a proper burial in the Mosul cemetery.

BAGHDAD — Violence and military operations claimed the lives of more than 16,000 civilians in Iraq last year, a research group said Thursday, making it one of the deadliest years for war-weary Iraqis since the 2003 U.S.-led invasion.

In its annual report, the London-based Iraq Body Count reported that 16,361 Iraqi civilians died in 2016. The northern province of Nineveh was the worst hit, with 7,431 people killed. The capital, Baghdad, was next with 3,714 civilians killed, the research showed.

Ninevah's capital, Mosul, fell to the Islamic State group in mid-2014 along with much of northern and western Iraq. Iraqi troops have since dislodged IS militants from major areas in a massive operation that started in mid-October.

Iraqi forces advancing from the north and east converged in Mosul on Thursday. The U.S. special envoy to the anti-IS coalition, Brett McGurk, called the advance a "milestone" in a statement posted on Twitter. Brig. Gen. Haider Fadhil of Iraq's special forces confirmed the advance.

Iraq's special forces have largely been leading the push in Mosul's east, while the Iraqi army has been advancing in the north of the city. Iraqi forces have retaken around a third of Mosul since the operation began in mid-October.

Iraq Body Count documents deaths from militants shooting captives, other gunfire, suicide attacks, bombings, air attacks and shelling. Last year, the greatest causes of death were the shooting of captives and other gunfire, which accounted for more than half of all civilian deaths, it said.

The group began documenting civilian deaths in Iraq after 2003, and relies on media reports, non-governmental organizations and Iraqi government sources. The report said 17,578 people were killed in 2015 and 20,218 in 2014.

The report comes only days after the United Nations in Iraq released a report that found 6,878 civilians were killed by violence in 2016. The U.N. mission said the numbers didn't include casualties among civilians in Iraq's western Anbar province for the months of May, July, August and December. It said it was hindered from verifying casualty numbers in conflict areas and from secondary effects of violence.

The deadliest IS attack came in July, when a massive suicide bombing in a bustling market area in central Baghdad killed almost 300 people, the bloodiest single attack in the capital in 13 years of war.