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.

A key test of whether the relationship can be salvaged comes next week when Secretary of State Rex Tillerson becomes the first Trump Cabinet member to visit Russia.

British Foreign Minister Boris Johnson also had planned to visit Russia this coming week, but decided Saturday to cancel the trip because of the fast moving events in Syria. Johnson, who condemned Moscow’s continued defense of Assad, said Tillerson will be able to give a “clear and coordinated message to the Russians.”

At the United Nations on Friday, 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.

The U.S. ambassador to the U.N., Nikki Haley, said the world is waiting for the Russian government “to act responsibly in Syria” and “to reconsider its misplaced alliance with Bashar Assad.”

Trump spoke by telephone Friday with Saudi Arabia’s King Salman, who reaffirmed strong support for the military strike and thanked the U.S. president for his “courageous” action, according to statements issued Saturday by the White House and the official Saudi Press Agency.

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.”

The Turkish foreign minister, whose country is a strong backer of the Syrian opposition, said the U.S. missile strikes were not enough. Mevlut Cavusoglu said Saturday that the U.S. intervention was only “cosmetic” unless it removes Assad from power. He said the most ideal process would be a political solution that leads to a transitional government.