The tally by the policy group also could be cited as part of possible international war-crimes cases against the regime of Syrian President Bashar al-Assad.

The Global Public Policy Institute (GPPI) said it had “credibly substantiated” 336 uses of chemical weapons, ranging from nerve agents to crude but dangerous chlorine bombs.

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Almost all the attacks — 98 percent — were attributed to Assad’s military or allied forces, including loyalist militias known as the Tiger Forces that also have the backing of Russia. The rest of the attacks were attributed to the Islamic State, which once held major parts of Syria.

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The GPPI analysis begins Dec. 23, 2012 — months after then-President Barack Obama’s declaration that use of chemical weapons against Syrian civilians would be his administration’s red line.

The researchers said they based their findings on witness statements and post-attack analysis, including reports of the effects from the apparent chemical agents and how the weapons were delivered on the attack sites.

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“The Assad regime did not merely ‘get away’ with its use of these banned weapons,” said the report. “It succeeded in using them for strategic ends.”

With Syria’s rebels on the verge of defeat and their former Gulf Arab backers reopening embassies in Damascus, Assad appears to be moving out of diplomatic isolation.

The United States remains a staunch opponent of Assad, although Washington holds little leverage over Syria. President Trump announced last month plans to withdraw U.S. forces from Syria. Trump’s claims that the Islamic State has been defeated, however, have brought sharp criticism from even political allies.

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In the aftermath of a 2013 nerve agent attack on a Damascus suburb, Obama pulled U.S. warplanes back from the brink after a last-minute deal that was meant to see Assad relinquish his chemical stockpiles.

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More than 72 tons were destroyed, but the attacks did not stop. The GPPI report said many of the subsequent attacks used chlorine, which turns into hydrochloric acid when inhaled. Exposure can damage the victim’s respiratory system and can lead to death in some cases.

Trump has twice ordered military action against Syrian government targets in the wake of high-profile chemical attacks, one on the northern town of Khan Sheikhoun and the other in the Damascus suburb of Douma.

There has been no recorded use of chlorine weapons in Syria since the last U.S. missile strike on April 14.

“The more we looked at the patterns associated with their use, the more we came to understand chemical weapons not as some special, separate evil, but as a key capability of the Syrian military as part of its broader campaign of indiscriminate violence,” said Tobias Schneider, who led the GPPI research team.

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Medical workers and first responders in opposition-held areas say they have treated more than 5,000 people for suspected chemical exposure since 2012, adding strain to an already buckling health system. At least 188 people have died after chlorine attacks, according to estimates by medical workers and first responders.

In interviews with The Washington Post, doctors described the chaos they sparked.

“It felt like psychological torture. We just couldn’t keep up,” said one who had worked in the opposition-held town of Jobar, before it was recaptured by the Syrian government in March.

“The bombs were bad enough, but when those other attacks started, we didn’t know what to do.”

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Chemicals, he said, brought a different type of fear.

Reports that another town had been hit would glue colleagues to their phones, with WhatsApp messages rolling in and describing symptoms the doctor already knew well.

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“We learned what chemicals do to a body and why we should fear them. They made people crazy. They made people terrified. You know, it broke the spirit,” the doctor said.

According to the data, Syria’s army has consistently prioritized striking population centers over front lines, even in the face of defeat on the ground.

“The strategy worked,” said Schneider. “It’s hard to imagine other regimes facing similar challenges, looking at places like Sudan, are not studying the Syrian example closely.”

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