– U.N. investigators have linked Russian forces to a possible war crime in Syria for the first time, reporting Tuesday that a Russian plane was responsible for airstrikes on a market last year that killed scores of civilians.

The plane carried out a series of attacks in November on the town of Al Atarib, west of Aleppo, killing at least 84 people and injuring more than 150, the U.N. Commission of Inquiry on Syria said.

The strikes may not have specifically targeted civilians, the panel ruled, but the use of unguided blast bombs in a densely populated area could amount to a war crime on the part of Russia, which has played a crucial role in backing the Syrian government.

The finding formed part of the panel’s 15th report on the conflict in Syria, which also said that the Syrian government had used chemical weapons in rebel-held areas of Damascus and that the U.S.-led coalition had inflicted heavy casualties in airstrikes aimed at the Islamic State of Iraq and Syria.

“All parties share guilt for completely disregarding the rules of war and for failing to adequately protect civilians,” said Paulo Sérgio Pinheiro, the panel’s chairman.

U.N. investigators had previously reported Russia’s critical role in the war in the two years since it stepped in to rescue President Bashar Assad’s faltering army, but a panel member, Hanny Megally, said this was the first time the commission had been able to nail down Russian involvement in a specific incident.

The panel cited evidence from early warning observers in Syria, who tracked the fixed-wing aircraft from the Russian air base at Humaimim, 100 miles from Al Atarib, until its attacks in the early afternoon, when the town’s market was crowded with people who had left work.

The panel also rejected the U.S.-led coalition’s account of multiple airstrikes last March on a school building in Raqqa Province, which investigators said killed at least 150 of the 200 civilians who were housed there after fleeing fighting elsewhere. The panel said it had found no evidence to support the coalition’s claim that the school was occupied by ISIS fighters.

The coalition attack did not amount to a war crime because it had no intent of hitting a civilian target, the panel concluded, but had violated international law by failing to take adequate precautions to protect civilians.

The international coalition had also inflicted countless civilian casualties in daily airstrikes on ISIS fighters in the city of Raqqa, launching attacks even though the militants were using civilians as human shields, the panel said.

The commission also faulted the coalition-backed Syrian Democratic Forces over their internment of about 80,000 civilians who had fled the fighting around ISIS strongholds in Raqqa and Deir al-Zour to vet them for possible links to the jihadis.

They continued to keep thousands of internally displaced people in camps in what the panel said amounted to arbitrary and unlawful detention.

Commission members said Tuesday that they planned to work vigorously on behalf of the victims but emphasized “there can be no trade-off between justice for the victims and a viable political solution” to the conflict.