Secretary of State Rex Tillerson said Thursday night that the U.S. didn't seek approval from Russia before launching missile strikes against a Syrian airfield, and instead only warned Russia that the strike was imminent.

"We sought no approval – we sought no approval from Moscow or at any other level within the Russian infrastructure," Tillerson told reporters late Thursday night at President Trump's resort home in Mar-a-Lago, Fla.

Both Tillerson and national security adviser H.R. McMaster stressed that Russia was essentially warned to get out of the way, part of the deconfliction process both countries use to make sure each side knows what the other is doing.

"This was strictly following the rules that we have put in place in agreement with the Russian military to de-conflict, because our target in this attack was not Russian," Tillerson said. "It was not the Russians. It was not their forces nor any Russian individuals. Our target was this airfield and the Syrian regime."

"[T]he purpose was not to receive permission" from Russia, McMaster said. "The purpose was to reduce the chances of Russian casualties."

Tillerson also stressed that there were "no contacts made with Moscow with President Putin" about the attack, and that the deconfliction channel involves other officials in the Russian military.