Washington • President Donald Trump said Monday that his administration would be making “major decisions” about its response to a suspected chemical attack in Syria within the next 24 to 48 hours, decrying the action as “atrocious” and “horrible.”

“We are very concerned when a thing like that can happen,” Trump said at the outset of a Cabinet meeting while reporters were present. “This is about humanity, and it can’t be allowed to happen.”

U.S. officials said Sunday that they were weighing options to strike Syrian government targets after at least 40 people were killed in the opposition-held town of Douma, roughly 10 miles from the Syrian capital.

Trump said Sunday on Twitter that there would be a “big price to pay” for the attack. His comments on Monday were his first publicly spoken remarks on the subject.

“If it’s the Russians, if it’s Syria, if it’s Iran, if it’s all of them together, we’ll figure it out,” Trump said.

Russian Foreign Minister Sergei Lavrov said Monday that Russian aid workers had visited the area and found no evidence that chemical weapons were used.

Russia is Syria’s main military partner and ally and has protected Syrian President Bashar Assad both militarily and diplomatically for years.

Russia helped the United States negotiate an agreement with Assad five years ago that was supposed to rid the country of chemical weapons, and the United States and other nations have held Russia responsible for allowing Assad to retain and use these weapons.

Asked by a reporter if he had any doubt who was behind the attack, Trump said: “To me there’s not much doubt, but the generals will figure it out.”

He said “nothing is off the table” when asked if U.S. military action is an option.

Trump said it has been “very hard to get people in” to determine what happened, which he said was a sign of Syria’s culpability.

Trump’s comments came as the U.N. Security Council was preparing to meet in an emergency session Monday to discuss the suspected chemical attack.

The Security Council meeting is shaping up to be a rematch of previous debates on civilian casualties in Syria. Though the council unanimously approved a cease-fire resolution in February, no truce has ever stuck.

Russia voted for the cease-fire but has repeatedly used its veto power as a permanent member to block any measure that threatens a Syrian offensive against rebels, largely to protect the government of Assad.

Russia wants to preserve access to its only naval base in the Middle East and preserve its influence in the region through Assad.

The Washington Post’s Carol Morello contributed to this report.