Russian President Vladimir Putin has condemned US cruise missile strikes on Syria as illegal, warning the move would further damage already battered US-Russia relations which Moscow had hoped President Donald Trump would revive.
US officials said they had informed Russian forces ahead of the strikes - intended to punish the Syrian government for what they say was a chemical weapons attack earlier this week - and had avoided hitting Russian personnel.
Satellite imagery suggests the Shayrat air base that was struck in western Syria is home to Russian special forces and military helicopters, part of the Kremlin's effort to help the Syrian government fight Islamic State and other militant groups.
Russia's main air base and a naval facility were not hit.
Moscow had been hoping to co-operate with Trump to jointly fight Islamic State in Syria, a move it was banking on to boost US-Russia ties which are at a post-Cold War low. After the US strikes, that task now looks harder.
"President Putin views the US strikes on Syria as aggression against a sovereign state in violation of the norms of international law and on a made-up up pretext," said a Kremlin statement.
"This step by Washington will inflict major damage on US-Russia ties."
Putin, a staunch ally of Syrian President Bashar al-Assad, was holding a meeting of Russia's Security Council to discuss the strike on Friday afternoon and the Russian Foreign Ministry called for an emergency meeting of the UN Security Council.
A foreign ministry statement said Moscow was suspending a Syrian air safety agreement with the United States originally drawn up to ensure that the two countries' planes did not collide.
"It's clear to any specialist that the decision to launch a strike was taken in Washington before the events in Idlib (the province where the gas poisoning took place) which were simply used as a pretext for a show of force," the ministry said.
Dmitry Peskov, Putin's spokesman, told reporters the US strikes had been conducted to help rebel groups fighting Assad.
Russia would keep military channels of communication open with Washington, but would not exchange any information through them, he added.
When asked whether Russia had deactivated its own anti-missile defence systems in Syria before the missile strike, Peskov declined to comment.
The Russian Defence Ministry meanwhile mocked the effectiveness of the US strikes, saying only 23 missiles had found their targets. It was unclear where another 36 had landed, it said, promising Syrian air defences would now be beefed up.
A Russian frigate armed with Kalibr cruise missiles sailed through the Bosphorus en route to the eastern Mediterranean in the early hours of Friday morning, according to pictures taken by Turkish bloggers for their online Bosphorus Naval News project.
It was unclear if that was related to the US strikes.
