U.N. and African Union peacekeeping forces in East Africa have repeatedly allowed their weapons to fall into the hands of armed groups responsible for much of the region’s violence, according to a report by a Geneva-based research group.

The report by the Small Arms Survey, published by the Washington Post, concluded that more than 500 weapons, including heavy machine guns and mortars, as well as nearly 1 million rounds of ammunition, were taken from peacekeeping forces in Sudan and South Sudan over the past decade.

The arms were seized from peacekeeping patrols, bases and supply convoys in at least 20 separate incidents between 2005 and 2014, the report said.

Eric Berman, a former U.N. peacekeeper and principal author of the report, said that the weapons seizures have undermined security in eastern Africa and that the actual losses probably exceed those documented in the report.

“The scale and scope is larger than what a lot of folks expected,” Berman said.

The report was funded in part by the State Department and was delivered to the United Nations on Tuesday, Berman said.

A senior U.N. official involved in peacekeeping efforts said in an e-mail that the study “sheds light on issues that have not been adequately addressed in the past,” but added that many of the report’s criticisms are overstated and that its findings are “two years behind the curve.”

The official said that the United Nations has taken steps over that period to improve the effectiveness of its peacekeeping units and that the number of weapons lost by those forces is “not the same order of magnitude as the 2.9 million small arms and over 1.5 billion rounds in circulation in Sudan [and] South Sudan over the past decade.” The official spoke on the condition of anonymity, citing the sensitivity of the issue.

The study focuses on weapons held by the roughly 250,000 troops deployed by the African Union and the United Nations to Sudan and South Sudan since peacekeeping operations began there in 2005.

That effort is aimed at stemming violence in a region where millions of people have been killed in border disputes, competition over oil supplies, and ethnic and religious conflicts — tensions that led to the creation of South Sudan as a separate state in 2011.

According to the United Nations, there are 6.9 million people in need of humanitarian assistance in Sudan and 1.4 million displaced people in South Sudan. The United Nations is involved in 16 peacekeeping missions around the world. By the end of last year, more than 1 in 4 of those troops were deployed to Sudan and South Sudan.

Losses of weapons and ammunition have been far greater in other conflicts. The Islamic State militant group in Iraq and Syria, for example, amassed an arsenal including tanks and antiaircraft weapons after overrunning U.S.-equipped forces in Mosul and other Iraqi cities last year.

But Berman said the losses by peacekeeping units have been overlooked as a factor hindering efforts to curb violence in regions beyond the more high-profile counterterrorism campaigns.

Berman, managing director of the Small Arms Survey, said he began examining the issue in 2008, shortly after two attacks in the Darfur region of Sudan ended with rebel groups seizing significant quantities of weapons from peacekeepers.

“Those two incidents within the span of six months gave me the opportunity to start asking some other questions,” Berman said. “Were these outliers? Was there more to it, and was this a bigger problem?”

Berman said that the amount of equipment taken is most likely understated “due to the lack of transparency in reporting” and a reluctance to criticize countries that are willing to contribute peacekeepers.

“There’s a bias against embarrassing troop-contributing countries,” he said. “There’s a focus on the safety of the men, while the weapons and the equipment are often not spoken of.”

Bangladesh, India and Pakistan have been the largest contributors of peacekeeping soldiers, Berman said. He noted that some U.N. officials and military leaders argue that a loss of weapons is inevitable in a hostile environment.

One of the largest losses by peacekeepers in Sudan came in 2008, when a shipment of ammunition to units in Nyala was attacked, Berman said. The report indicates that more than 600,000 rounds, or 12 1/2 tons of ammunition, were taken — enough to support 800 rebels for one year.

Berman said he hopes the report will encourage further research and vigilance in monitoring weapons brought into conflict zones by peacekeepers. The report calls for additional training for units on managing weapons stockpiles and more thorough reporting of arms inventories after their missions are done.

Enhanced transparency would allow organizations such as the Small Arms Survey to potentially track the seized weapons outside the conflict zones where they were taken, Berman said.

“What we’ve achieved is getting people interested in this and willing to fund additional research,” Berman said, adding that the United Nations and some countries that contribute troops have been more willing to engage with the topic since he approached them with his findings.

“It’s a sea change from where we were four or five years ago, where it was either discounted or considered risque,” he said. “We’re eager to explore this further.”