Smoke billows after a February airstrike on the besieged Eastern Ghouta region on the outskirts of Damascus. Rebel forces in the area surrendered in early April. (Ammar Suleiman/AFP/Getty Images)

The United Nations said Wednesday that Syrian army and rebel forces committed war crimes as they fought over a Damascus suburb gripped by the longest siege in modern history.

Hundreds of civilians were killed earlier this year during the government’s months-long offensive to push rebel groups from their last foothold near the capital, Eastern Ghouta.

The area lay in ruins by the time the rebels surrendered in early April.

In a 23-page report released Wednesday, investigators from the U.N. Commission of Inquiry said the Syrian military campaign to seize Eastern Ghouta after five years of rebel control involved indiscriminate attacks on civilian homes, markets and hospitals, forcing a besieged and terrified civilian population underground. 

Under international law, the panel said, those attacks amounted to war crimes.

“It is completely abhorrent that besieged civilians were indiscriminately attacked, and systematically denied food and medicine,” Paulo Pinheiro, who leads the commission, said in a news release.

After Eastern Ghouta, the government has turned its attention to the remaining rebel-held pockets of the country. Victory for President Bashar al-Assad is all but assured. 

Although it is unlikely that a final death toll from the Ghouta offensive will ever be known, relief organizations said at the time that the relentless bombing by Syrian and allied forces had killed more than a thousand people and wounded almost five times as many. During the offensive’s final weeks, the few hospitals standing were treating patients with the dregs of their supply cupboards, bandaging wounds with rags and conducting operations without anesthetic. 

It was, Doctors Without Borders said, “an outrageous, relentless mass casualty disaster.” 

About 140,000 people had been displaced from their homes by the time the government raised its flag in Eastern Ghouta after the rebels’ April 8 surrender.

The surrender was precipitated by an alleged chemical attack by government forces that killed scores.

While the incident is being examined by a global watchdog linked to the United Nations, the independent commission appeared to have removed its own preliminary findings from an earlier version of the report. The New York Times said Wednesday that it had obtained a draft version which dedicated 20 paragraphs to evidence of extensive chemical weapons usage by Syrian government forces, saying the attacks constituted “one of the most grim patterns of attack documented during the period under review.”

The U.N. panel also said that hard-line rebel forces had arbitrarily arrested and tortured civilians in areas under its control. In the dying weeks of the military campaign, they also intensified indiscriminate reprisal attacks on densely populated areas controlled by the government, killing and wounding hundreds, the panel said.

“Such actions by armed groups and members of terrorist organisations also amount to war crimes,” Hanny Megally, a member of the commission, said in the news release.

With the U.N. Security Council deadlocked over the Syria crisis, the Commission of Inquiry has emerged as one of the strongest critics of the country’s warring parties, condemning human rights violations on the battlefield and inside government and opposition-held jails. 

Its report was based on 140 interviews, as well as photographs, videos, satellite imagery and medical records. 

The panel also criticized how the government has treated civilian survivors of the Eastern Ghouta offensive, saying it has detained tens of thousands who had chosen to leave the enclave for government-controlled territory.

Of the approximately 95,000 people taken for security screening to hastily constructed displacement camps, the United Nations said, about 31,000 are still unable to leave.