Secretary of State Rex Tillerson said Thursday that there is “no doubt” Syrian President Bashar Assad is responsible for the suspected chemical weapons attack that killed dozens of people, including children, earlier this week — and that diplomatic steps to remove him from power are underway.

“There is no doubt in our minds and the information that we have supports that Syria and the Syrian regime under the leadership of President Bashar al-Assad are responsible for this attack,” Tillerson said in a press briefing at Palm Beach International Airport. “And furthermore, I think it is very important that the Russian government consider very carefully their continued support for the Assad regime.”

Assad’s “role in the future is uncertain, clearly,” Tillerson said. “And with the acts that he has taken, it would seem there would be no role for him to govern.”

For Assad to leave, the secretary said, would require an “international community effort” that would include the defeat of the Islamic State group in Syria, stabilization of the war-torn country and “a political process that would lead to Assad leaving.”

When asked if President Trump would be organizing an international coalition to remove Assad, Tillerson said, “Those steps are underway.”

Tillerson speaks to reporters at Palm Beach International Airport in West Palm Beach, Fla., on Thursday. (Joe Skipper/Reuters)

He added: “We are considering an appropriate response for this chemical weapons attack, which violates all previous U.N. resolutions, which violates international norms and long-held agreements of parties including the Syrian regime, the Russian government and all other members of the U.N. Security Council.”

Speaking to reporters aboard Air Force One, Trump suggested Assad may have to leave.

“He’s there, and I guess he’s running things,” the president said, on his way to meet Chinese President Xi Jinping at the U.S. president’s Mar-a-Lago estate. “So something should happen.”

Related: Trump hints at military action to retaliate against Assad

But Trump declined to offer specifics when pressed on what the U.S. response would be to the attack in Syria, saying only it “shouldn’t have happened, and it shouldn’t be allowed to happen.”

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At a joint press conference with King Abdullah II of Jordan on Wednesday afternoon in Washington, Trump condemned the attack, saying, “It crossed a lot of lines for me.”

“A chemical attack that was so horrific in Syria against innocent people, including women, small children and even beautiful little babies. Their deaths were an affront to humanity,” Trump said. “These heinous actions by the Assad regime cannot be tolerated.”

Speaking in Turkey last week, Tillerson said, “The status and the longer-term status of President Assad will be decided by the Syrian people.”

Those comments drew sharp criticism from some Republican lawmakers, including Arizona Sen. John McCain, who called it “one of the more incredible statements I’ve ever heard.”

“Syrian people cannot decide the fate of Assad or the future of their country when they are being slaughtered by Assad’s barrel bombs, Putin’s aircraft and Iran’s terrorist proxies,” McCain said in a statement. “U.S. policy must reflect such basic facts.”

Florida Sen. Marco Rubio said Tillerson’s remarks may have given Assad an opening to carry out this week’s attack without fear of reprisal.

“In essence [it’s] almost nodding to the idea that Assad was gonna get to stay in some capacity,” Rubio said in a radio interview on Wednesday. “I don’t think it’s a coincidence that a few days later we see this.”

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