Defense chief Mattis says Syria will pay a big price if it uses gas again

Defense Secretary Jim Mattis said Syria will pay a "very, very stiff price" if it uses chemical weapons again.

The remarks from Mattis were the strongest yet from the Pentagon on the April 4 chemical attack U.S. officials say Syrian President Bashar Assad ordered that killed as many as 100 civilians. The Pentagon responded by firing 59 Tomahawk cruise missiles on Thursday at the air base where the chemical attack originated.

"The Syrian regime should think long and hard before it again acts so recklessly in violation of international law against the use of chemical weapons," Mattis said.

Mattis pointedly included chlorine gas a chemical weapon. Pentagon officials last week noted that the Syrian army used the industrial gas against its citizens as recently as March 25.

Hours before Mattis' briefing, the National Security Council released a report that showed evidence that the nerve agent sarin had been used in the attack. The evidence includes intercepted communications, spy satellite imagery and laboratory analysis. The report also blames Russia, Syria’s patron, for attempting to cover up Syria’s illegal use of chemical weapons.

The news conference Tuesday at the Pentagon was Mattis’ first and amounted to a full-court press with the White House, State Department and Pentagon confronting Russia and Syria within hours. Mattis was joined by Army Gen. Joseph Votel, commander of U.S. Central Command.

The cruise missile attack had a singular purpose and was not a "harbinger of some change in our strategy" that indicates broader U.S. involvement in the Syrian conflict, Mattis said.

Votel said 57 of the 59 missiles hit their targets. Mattis estimated that the strike eliminated 20 Syrian warplanes and characterized Assad's air force as "not in good shape."

Mattis largely avoided questions about Russia's involvement, instead stressing Syria's responsibility for the chemical attack.

Syrian’s civil war has killed 400,000 people and displaced about 9 million. In August 2013, Assad’s regime unleashed sarin in an attack that killed 1,400 civilians. Syria, with Russia’s backing, agreed to turn over its chemical weapons stocks for destruction.

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The April 4 attack shows that it retains chemical weapons, and came amid Syrian government concerns that it could lose a key airfield to rebels.

Last week, Pentagon officials stopped just shy of implicating Russia in the chemical attack. Officials maintained that Russia, at minimum, had a responsibility to prevent its client state from conducting the attack. There are as many as 100 Russian personnel at the base.

Meanwhile, Secretary of State Russ Tillerson warned Russia on Tuesday in briefing in Italy to stop supporting Assad.