After a week of forcefully denying allegations his regime conducted strategic executions of 13,000 prisoners in a military prison outside Damascus over a four-year period, Syrian President Bashar Assad faces two new damning reports that document atrocities carried out by his government and its ally, Russia, in their final push to retake Aleppo from rebels in late 2016. The reports detail a coordinated use of chemical weapons by Assad’s regime and present evidence that Russian warplanes dropped bombs on civilian hospitals in Eastern Aleppo.

The first report, entitled “Breaking Aleppo,” which details the scale of the atrocities inflicted on the city, directly accused the Russian government of bombing civilian locations, including hospitals, which it had previously denied ever happened. Bombing such locations are seen as a violation of international humanitarian law.

Produced by the Atlantic Council, a Washington-based think tank, the report used satellite imagery, security camera videos, and social media accounts to reconstruct attacks against civilian hospitals in rebel-held areas of the city, dispelling accounts by Moscow last year that it had not bombed those locations.

“What we have been able to present now is a wealth of evidence confirming the targeting of civilian structures, namely hospitals, which in certain cases has been denied by the Russian Ministry of Defense,” Eliot Higgins, a senior fellow at the Digital Forensic Research Lab of the Atlantic Council, said.

The second report, published by Human Rights Watch, documents eight separate attacks by government forces involving the use of chlorine gas in rebel-held areas of Aleppo. All eight attacks took place between November 17 and December 13, as government forces, backed by Russian aircraft, pushed to recapture the key Syrian city. HRW says there were likely many more times when chemical weapons were used during the battle, but it documented only those for which it has evidence.

The eight attacks resulted in the death of at least nine civilians, including four children, as well as 200 injured.

Proof of the use of chemical weapons would amount to the most egregious breach of international laws yet by the Assad regime, already accused of multiple atrocities throughout its years-long civil war. Just three years ago Assad signed an international treaty that prohibits the use of such weapons.

This is not the first time Assad’s regime has been accused of using chemical weapons since agreeing in 2013 to relinquish the country’s chemical weapons stockpile. A U.N. panel concluded last year that the Syrian government had used chlorine canisters as weapons three times in 2014 and 2015 as the war with rebels waged on. Last August doctors warned that the frequent use of chemical weapons in the Syrian civil war risked “normalizing war crimes.” The 1993 Chemical Weapons Convention bans the use of the toxic properties of any chemical as a weapon.

“The pattern of the chlorine attacks shows that they were coordinated with the overall military strategy for retaking Aleppo, not the work of a few rogue elements,” Ole Solvang, deputy emergencies director at HRW, said in a statement. “The United Nations Security Council shouldn’t let Syrian authorities or anyone else who has used chemical weapons get away without consequences.”

This is how one Aleppo resident described the impact of chlorine: “The smell isn’t something you can handle. The moment you’re exposed to it, your throat burns, it’s like a fire rod going in. It won’t let you swallow or breathe. Your neck starts boiling. You feel nauseated. Your eyes burn and you are not able to control the tears. Eventually, you are not able to breathe. It’s not like having your nose and mouth blocked; rather, your body won’t let the air in anymore.

There have been calls for those conducting atrocities in Syria to be held accountable at the International Criminal Court, but considering a similar report from HRW was released over three years ago, also accusing the Syrian government of using chemical weapons, it is clear that bringing those responsible to justice is no simple task. Both China and Russia have blocked U.N. resolutions to refer Syrian atrocities to the ICC, and Assad has consistently denied use of chemical weapons, saying the evidence was fabricated.

Last month, in one of his last acts as president, Barack Obama tightened sanctions against Syria as a result of the U.N. findings. Obama had said in 2012 that the use of chemical weapons would be the “red line” which, if crossed, would lead to U.S. military intervention in the conflict. But when it was shown that sarin gas had been used by Assad’s regime in 2013, Obama failed to follow through on his promise.

While there is no evidence that Russia was directly involved in the use of chemical weapons in Aleppo, it was still complicit in the attacks, HRW contends. A report by the U.N.-appointed Joint Investigative Mechanism previously found that helicopters used in the chlorine attacks were operating from the Hmeymim airbase, which was under Russian control.