The Pentagon chief says it's clear the Syrian government is to blame for a chemical weapons attack targeting civilians.

FOX's Jared Halpern has more from Washington:

Secretary of Defense James Mattis says there's no doubt the Syrian government is responsible for last week's chemical weapons attack, leading to a U.S. missile strike on a Syrian airfield:

(Mattis) "It was very clear that the Assad regime planned it, orchestrated it and executed it. And beyond that we can't say right now."

Mattis says intelligence hasn't determined if Russia had advance knowledge of the chemical attack.

Secretary of State Rex Tillerson is in Moscow for meetings with his Russian counterpart. Mattis telling reporters rising tensions between the U.S. and Russia over Syria will not spiral out of control.

In Washington, Jared Halpern, FOX News.

Follow Jared Halpern on Twitter: @JaredHalpern