Defense Secretary James Mattis told reporters at the Pentagon Friday that the U.S. and its allies carried out a "heavy" one-time strike on Syria — double the size of last year's offensive — that President Donald Trump was authorized to order under the Constitution.
"The United States has a vital interest to defend our interests and in specifically deterring the use and proliferation of chemical weapons," Mattis said in a news conference after the strikes were completed.
Assad has used "chemical weapons to murder women, children and other innocents.
"We and our allies find these atrocities inexcusable."
Mattis said the U.S. was convinced that Syria used chlorine gas on its citizens, possibly even sarin gas, which has been used in the past.
"Tonight, France, the United Kingdom and the United States took decisive action to strike the Syrian chemical-weapons infrastructure," Mattis said. "Clearly, the Assad regime did not get the message last year.
"This time our allies and we have struck harder.
"Together, we have sent a clear message to Assad and his murderous lieutenants that they should not perpetrate another chemical-weapons attack for which they will be held accountable."
Army Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said that the airstrikes began at 9 p.m., hitting three targets in or near Damascus that produced, tested or stored chemical weapons.
Russia was not consulted or informed of the strike, he said, and targets were specifically chosen to avoid hitting Moscow's operations or forces.
"We selected targets that would minimize the risk to innocent civilians," Dunford said.
"Important infrastructure was destroyed, which will result in a setback for the Syrian regime — and they will lose years of research and development data, specialized equipment and expensive chemical-weapons precursors," Dunford said.
"The strike was not only a strong message to the regime that their actions were inexcusable, but it also inflicted maximum damage without unnecessary risk to innocent civilians."
Mattis said that any further strikes would "depend on Mr. Assad, should he decide to use more chemical weapons in the future."
"But right now, this is a one-time shot —and I believe that it sent a very strong message to deter him from doing this."
The secretary also warned of a "significant disinformation campaign over the coming days by those who have aligned themselves with the Assad regime" — hinting at Russia — and promised another briefing early Saturday.