Updated 2:54 p.m. | President Donald Trump is prepared to again strike Syria if its president, Bashar Assad, launches another chemical weapons attack, a senior administration official said Saturday.

“If this act does not succeed, we will act again,” the senior official said, referring to Friday night’s cruise missile strikes on Syrian government targets.

Despite Trump declaring “Mission accomplished!” earlier in the day in a tweet, the official told reporters success would be defined by Assad not using chemical weapons again.

A perfectly executed strike last night. Thank you to France and the United Kingdom for their wisdom and the power of their fine Military. Could not have had a better result. Mission Accomplished!

— Donald J. Trump (@realDonaldTrump) April 14, 2018

Senior administration officials said Saturday they believe the U.S.-French-British strikes, which were aimed at Assad’s chemical weapons infrastructure, hit their intended targets. But an opposition group on the ground there raised doubts as the sun rose in Syria.

Vice President Mike Pence said the operation “degraded and crippled” and “significantly eroded” the Assad government’s ability to use chemical weapons. He also defended the mission to reporters with him in Peru, saying, “This was the morally right act to take,” according to a pool report.

He also had this message for Russia, one of Assad’s key backers: “You’re on the wrong side of history.” The Kremlin needs to “live up to the commitments they made,” he said of Russia’s vow to remove Assad’s chemical arsenal.

“You’re known by the company you keep,” Pence said. 

French and British leaders, who joined the U.S. in ordering Syria strikes Friday night, have assured Trump they, too, are “willing to do more militarily,” the senior official said.

What’s more, the United States and its allies have “evidence” that Assad’s forces used both chlorine and sarin gas in last weekend’s chemical attack on a rebel-held Damascus suburb, the senior administration official said.