United Nations investigators formally accused the Syrian government Wednesday of using the banned nerve agent sarin in a deadly chemical weapons attack in April that left dozens of civilians dead and hundreds more wounded.

The daybreak attack, the investigators said in a report, was one of more than 20 government assaults involving chemical weapons since March 2013, most of them targeting families with no part in the conflict.

The United Nations Commission of Inquiry on Syria is tasked with investigating alleged war crimes that have taken place during the six-year conflict. But it has no capacity to prosecute any party, underscoring the geopolitical constraints that hamstring the world's response to the war.

The commission's report marked first time that a U.N. body has explicitly accused the Syrian government of using sarin, a chemical that pushes the nervous system into overdrive and can kill in minutes.

[Global watchdog confirms use of sarin in Syrian chemical attack]

Video footage from the scene of the attack on the northern village of Khan Sheikhoun showed men, women and infants convulsing uncontrollably. In many cases, they had no idea what had hit them — sarin is colorless, odorless and tasteless.

The attack killed at least 83 people, dozens of them women and children. According to investigators, some died in their beds. A single mother who had left her house early to work said she returned to find all of her four children dead.

Images of the youngest casualties are believed to have figured in President Trump's decision to order missile strikes on a Syrian government airstrip days later, marking the first direct American military intervention against Syrian President Bashar al-Assad.

The Syrian government and its Russian backers had insisted that the Khan Sheikhoun attack was the fault of opposition forces in the area, or that it was entirely fabricated. The inquiry found no supporting evidence for either claim.

[Chemical attack that drew U.S. response was just one in a series]

Diplomacy over the Assad government's use of chemical weapons has been thorny, resulting in deadlock at the U.N. Security Council as the Syrian president's key backers have blocked resolutions to punish his armed forces.

Despite an internationally backed effort to remove the Syrian government's chemical weapons stockpiles, U.S. intelligence officials believe that it retains a significant quantity that could still be used for attacks on civilians.

The U.N. commission also criticized both a U.S.-led coalition and jihadist groups it is battling, accusing them of possible war crimes in Syria. The condemnation highlighted the breadth of atrocities in a war that has killed nearly half a million people and driven millions more to flee as refugees.

[Mounting claims of civilian deaths in U.S. airstrike in Syria]

As U.S.-backed forces fight their way through the Islamic State stronghold of Raqqa, the coalition faces mounting allegations of civilian casualties from its airstrikes on heavily armed extremist groups in Syria and Iraq. In a detailed timeline of a March attack on a mosque in the northern Syrian town of Jinah, the commission said the coalition had neither taken appropriate measures to protect civilians nor provided evidence to back up its claim that the mosque was being used as a meeting place for senior al-Qaeda leaders.

"Information gathered by the Commission does not support the claim that any such meeting was being held at that time," the U.N. report said. "Interviewees described the gathering as strictly religious, and explained that most attendees were Al-Jinah residents, and that many of them were internally displaced persons, with the exception of some residents from neighbouring towns."

At least 38 people were killed in the attack, including a woman and three boys ranging from 6 to 13 years old.

[Chemical weapons activity monitored at Syrian air base]

The coalition has repeatedly emphasized that it takes extensive precautions before launching any strike that may affect civilians. On Wednesday, the commission concluded that these procedures were not followed adequately in Jinah.

Although the targeting team had information on the target three days before the strike, the inquiry said that the expected additional verification processes were not completed.

The commission also accused Islamic State and al-Qaeda-linked rebels of targeting religious minorities with car bombs, snipers and kidnapping.

Violence, it said, continues to be carried out "in blatant violation of basic international humanitarian and human rights law principles, primarily affecting civilians countrywide."

Read more:

Sarin was used in April attack on Syrian civilians, global watchdog confirms

For Trump, sarin in Syria prompted a different reaction than other chemicals

Using chemical weapons is risky. So why did Syria use sarin?

Today’s coverage from Post correspondents around the world

Like Washington Post World on Facebook and stay updated on foreign news