ARLINGTON, Va. — Pentagon leaders made clear that the strikes in Syria announced by President Trump tonight were over almost as soon as they began, with Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford telling reporters “this wave of airstrikes is over” and Defense Secretary James Mattis calling them a “one-time shot.”

“The targets that were struck and destroyed were specifically associated with the Syrian regime’s chemical weapons program,” Dunford said. “We also selected targets that would minimize the risk to innocent civilians.”

Mattis, alongside Dunford, noted that “the Syrian people have suffered terribly under the prolonged brutality of the Assad regime,” including the April 7 attack on Douma in which the regime “decided to again defy the norms of civilized people, showing callous disregard for international law by using chemical weapons to murder women, children and other innocents.”

Mattis added that the U.S. “has an important national interest in averting a worsening humanitarian catastrophe in Syria, and specifically deterring the use and proliferation of chemical weapons.”

Today’s strike came after reported clashes in the administration between those advocating for sustained military action, including Trump and National Security Advisor John Bolton, and the Pentagon, which was concerned about potential escalation.

“The purpose of our actions tonight is to establish a strong deterrent against the production, spread, and use of chemical weapons. Establishing this deterrent is a vital national security interest of the United States,” Trump said in a press statement in the White House’s Diplomatic Room. “The combined American, British, and French response to these atrocities will integrate all instruments of our national power — military, economic, and diplomatic. We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents.”

Mattis said the strikes, in conjunction with France and the United Kingdom, constituted “decisive action to strike the Syrian chemical weapons infrastructure.” He added that the coalition went “to great lengths to avoid civilian and foreign casualties.”

“But it is time for all civilized nations to urgently unite in ending the Syrian civil war by supporting the United Nations-backed Geneva peace process,” Mattis said.

Three targets were hit beginning at 9 p.m. EST: the Syrian government’s weapons-development Scientific Studies and Research Center and two chemical weapons storage facilities. Dunford said one facility west of Homs was assessed as “the primary location of Syrian sarin and precursor production equipment.”

Mattis said he’s “confident” Assad was behind the Douma gas attack, and is “not ruling out” sarin as one of the agents used in the assault.

State Department press secretary Heather Nauert told reporters earlier Friday that the United States, along with France and the UK, had proof of the chemical attack but was still determining the “exact” cocktail of chemicals used.

“I’m not going to say which day we absolutely knew there was proof, the attack took place on Saturday, we know for a fact it was a chemical weapon, we know that there are only certain countries, like Syria, that have delivery mechanisms and those types of weapons,” Nauert said.