Western powers have condemned Syria for unleashing a chemical attack on civilians in Khan Sheikhoun, a community in a rebel-controlled zone in northwestern Syria. While the details remain in dispute, and Syria denies using chemical weapons, multiple reports from hospitals and other eyewitnesses describe an airstrike followed by victims choking to death.

The Syrian Observatory for Human Rights put the death toll at 72, including many women and children. The World Health Organization said a chemical attack was likely because of the "lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death. Some cases appear to show additional signs consistent with exposure to organophosphorus chemicals, a category of chemicals that includes nerve agents."

The outcry leads us to revisit a 2014 claim from former Secretary of State John Kerry. Kerry said in a television interview that in Syria, "we got 100 percent of the chemical weapons out."

Syria had agreed in 2013 to an ambitious program to destroy its chemical stockpiles under international supervision, as part of a deal brokered by Russia. When Kerry spoke in July 2014, the process seemed far along. Based on reports from the Organization for the Prohibition of Chemical Weapons -- which later won the Nobel Peace Prize for its efforts -- we rated that claim Mostly True. There were caveats about incomplete information, but at the time, international experts said the claim largely held up.

Given recent events, we have pulled that fact-check (you can read an archived version here) because we now have many unanswered questions.

We don’t know key details about the reported chemical attack in Syria on April 4, 2017, but it raises two clear possibilities: Either Syria never fully complied with its 2013 promise to reveal all of its chemical weapons; or it did, but then converted otherwise non-lethal chemicals to military uses.

One way or another, subsequent events have proved Kerry wrong.

In fact, international investigators concluded last year that the Syrian government had gamed the system.

In October 2016, a joint effort by the United Nations and the Organization for the Prohibition of Chemical Weapons reported that Syrian Arab Armed Forces had dropped chemical-laden bombs four times between 2014 and 2015. (That conclusive evidence was not available at the time of the original fact-check. One of our principles is that we rate statements based on what is known at the time.)

The U.N. group also found that Islamic State units had fired shells filled with sulfur mustard (mustard gas) in an attack in 2015.

Syrian forces used chlorine gas in 2014 and 2015. Brian Finlay, president of the Stimson Center, a military and defense think tank in Washington, noted that Syria promised to rid itself of sarin, mustard and VX, a nerve agent. But chlorine-based chemicals present a different challenge.

"They can be used for perfectly legitimate and essential civilian purposes today, and repurposed tomorrow to perpetrate heinous crimes like those we witnessed in Syria this week," Finlay said.

In November 2016, the Organization for the Prohibition of Chemical Weapons pointed out the failure of the Syrian government to live up to the promises it made in 2013. The group’s executive committee "demanded that the Syrian Arab Republic comply fully with its obligations."

In the latest incident, the Russian government has suggested that Syrian aircraft had hit rebel chemical stockpiles. Military experts challenged that, saying whatever agent was involved, the way it spread wasn’t consistent with that explanation. The Syrian government has made the same argument about rebel stockpiles before. When pressed for details by international inspectors, it has provided none.

In the days and weeks to come, we will learn more about the recent attacks, but in the interest of providing clear information, we have replaced the original fact-check with this update.