In a strong appeal, Pope Francis said he was “horrified” by Tuesday’s slaughter of men, women and children in a chemical weapons attack in Idlib, Syria.

After his weekly General Audience in Saint Peter’s Square Wednesday before tens of thousands of pilgrims, Francis expressed his “strong abhorrence for the unacceptable massacre that took place yesterday in Idlib province, where dozens of civilians, including many children, were killed.”

At least 72 civilians were killed and hundreds more injured from an aerial bombardment that included the release of bombs of poisonous gas, causing victims to die from suffocation and muscle spasms.

“It’s just indescribable,” said a local witness to the attack, Othman al-Khani. “We saw people suffocating while their lungs were collapsing. The hardest was watching the children as we stood there unable to provide any sort of assistance, and medics sprayed them with water” to disperse the chemical substance.

Reports suggested that the symptoms of victims are consistent with those associated with sarin gas, which causes death by asphyxiation within a matter of minutes and is very difficult to detect. The Syrian government has allegedly used sarin gas on previous occasions.

The Syrian and Russian governments “flatly denied any responsibility” for the attack and the Russian defense Ministry denied carrying out any airstrikes on the Khan Sheikhoun area. For their part, Syrian officials “repeated blanket denials of ever having used chemical weapons,” and further denied targeting anyone except “terrorists.”

The Organization for the Prohibition of Chemical Weapons is investigating the incident, and the United Nations said it would inquire into the attack as a possible war crime, reports said.

“Horrified, we have witnessed the latest events in Syria,” Pope Francis said Wednesday. “I pray for the victims and their families, and I appeal to the conscience of those who have political responsibility, locally and internationally, to bring this tragedy to an end and give relief to that beloved population for too long exhausted by war.”

The Pope also encouraged the efforts of those who are working to provide assistance to the inhabitants of the region.

He also made reference to Monday’s suicide bombing of the St. Petersburg subway, which resulted in more than a dozen casualties.

“As I entrust to God’s mercy those who tragically died, I express my spiritual closeness to their families and to all those who suffer because of this dramatic event,” he said.

The alleged perpetrator of the attack, Akbarzhon Jalilov, a 22-year-old Kyrgyz-born Russian citizen, reportedly had ties to radical Islamist groups, and Kyrgyzstan intelligence services said that the Islamic State may have been involved in the terror attack.

The subway explosion killed 14 people and injured 49 more.

Follow Thomas D. Williams on Twitter