PALM BEACH, Fla. — The United States is vowing to keep up the pressure on Syria after the intense nighttime wave of missile strikes from U.S. ships, despite the prospect of escalating Russian ill will that could further inflame one of the world’s most vexing conflicts.

Standing firm, the Trump administration on Friday signaled new sanctions would soon follow the missile attack, and the Pentagon was even probing whether Russia itself was involved in the chemical weapons assault that compelled President Donald Trump to action. The attack against a Syrian air base was the first U.S. assault against the government of President Bashar Assad.

Much of the international community rallied behind Trump’s decision to fire the cruise missiles in reaction to this week’s chemical weapons attack that killed dozens of men, women and children in Syria. But a spokesman for Russian President Vladimir Putin warned that the strikes dealt “a significant blow” to relations between Moscow and Washington.

At the United Nations, Russia’s deputy ambassador, Vladimir Safronkov, strongly criticized what he called the U.S. “flagrant violation of international law and an act of aggression” whose “consequences for regional and international security could be extremely serious.” He called the Assad government a main force against terrorism and said it deserved the presumption of innocence in the chemical weapons attack.

U.S. officials blame Moscow for propping up Assad.

“The world is waiting for the Russian government to act responsibly in Syria,” Nikki Haley, the U.S. ambassador to the U.N., said during an emergency Security Council session. “The world is waiting for Russia to reconsider its misplaced alliance with Bashar Assad.”

Haley said the U.S. was prepared to take further action in Syria but hoped it wouldn’t be necessary.

The official Saudi Press Agency reported that King Salman complimented Trump in a telephone conversation for his “courageous decision.”

Saudi Arabia, one of the most vehement opponents of Assad, said the missile barrage was the right response to “the crimes of this regime to its people in light of the failure of the international community to stop it.”