“I believe this horrible memory will stay with me for the rest of my life.”

ambulances to Idlib, the Turkish Anadolu news agency reported.

Syrian opposition health minister Firas Jundi put the death toll at more than 100 civilians and said 500 others, mostly children, were sickened or burned by the gas.

“I believe this horrible memory will stay with me for the rest of my life,” Jundi told CNN.

If it is confirmed as a chemical attack, it would be the largest in Syria since August 2013, when sarin gas killed hundreds of civilians in Ghouta near Damascus. Reuters reported that the U.S. government believes sarin may have also been used in the attack Tuesday.

The Syrian anti-government activist group Idlib Media Center published photos of young children receiving medical treatment, and a video showed what appeared to be bodies of children lined up on a blanket.

The Syrian government of President Bashar Assad denied using chemical weapons, but the U.S. and international communities were unconvinced.

In a statement, Secretary of State Rex Tillerson took aim at Russia and Iran.

“There are reports of dozens dead, including many children. While we continue to monitor the terrible situation, it is clear that this is how Bashar al-Assad operates: with brutal, unabashed barbarism,” the statement said. “Those who defend and support him, including Russia and Iran, should have no illusions about Assad or his intentions. Anyone who uses chemical weapons to attack his own people shows a fundamental disregard for human decency and must be held accountable.”

The statement also called on the countries to act. “As the selfproclaimed guarantors to the cease-fire negotiated in Astana, Russia and Iran also bear great moral responsibility for these deaths.”

The New York Times quoted an unnamed State Department official, who said that it appeared Russia was unable or unwilling to hold the Syrian government to the cease-fire terms.

The official said the attack on civilians appears to be a war crime.

The suspect in a suicide bombing in a St. Petersburg subway train that killed 14 people was identified Tuesday as a Russian citizen born in Kyrgyzstan, officials said.

Russia’s Investigative Committee said it believes Akbardzhon Dzhalilov, 22, was responsible for the attack Monday in the country’s second-largest city. The investigators said Dzhalilov’s DNA was found on a bag containing a bomb that was discovered and defused at another subway station in St. Petersburg on the same day. There was no immediate claim of responsibility.

On Tuesday, German Chancellor Angela Merkel and French President François Hollande discussed with Russian President Vladimir Putin ways to boost anti-terrorism cooperation after the bombing.