The U.S. military — together with French and British forces — struck three targets inside Syria on Friday night, just days after Bashar Assad’s government allegedly carried out a chemical attack on a Damascus suburb and amid new U.S.-Russia tensions.

In a televised address, President Donald Trump announced that strikes against Assad’s forces were “now underway.”

“This massacre was a significant escalation in a pattern of chemical weapons use by that very terrible regime,” Trump said.

An hour later, Gen. Joseph F. Dunford Jr., chairman of the Joint Chiefs of Staff, said the strikes had ended, but Defense Secretary James Mattis warned Assad that there would be retaliation for future chemical attacks.

“Right now, this is a one-time shot and I believe it has sent a very strong message to dissuade him, to deter him from doing that again,” Mattis said.