The Russian government has sharply contested accounts by international leaders and witnesses that a deadly chemical attack in northern Syria last week was carried out by Syrian government forces. Here’s what the available evidence, including a declassified four-page American intelligence report, tells us about the reliability of the Russian account.

Whether There Was a Chemical Attack

Russian officials, including President Vladimir V. Putin, have publicly doubted whether a toxic attack even happened, and said that any chemical weapons in Syria belonged to insurgents fighting President Bashar al-Assad’s forces, not the government.

The White House has asserted that the Assad government carried out the attack, and that the Russians tried to cover it up by spreading “false narratives.”

There is no evidence that online video and photographs of the attack were fabricated, as Russia’s deputy envoy to the United Nations suggested last week. The images showed that scores of people, including children, died on April 4 in Khan Sheikhun, in northern Syria, suffering symptoms consistent with having breathed in some sort of nerve agent.