The US fired 59 Tomahawk missiles on a Syrian airbase in response to an alleged chemical weapons attack which killed civilians, drawing angry responses from Syria and its key ally Russia.
The US action on Thursday night killed six Syrian soldiers and nine civilians besides causing huge damage at the Shairat military base in Homs province in central Syria, news reports said.
Syria termed the missile barrage an "American aggression" and held consultations with Russia and Iran.
Russian President Vladimir Putin said the strikes were an "aggression against a sovereign state" and violated "international norms". The Kremlin warned it would hamper Washington's ties with Russia.
Within hours, Russia suspended a deal with the US to prevent mid-air collisions over Syria.
"The Russian side suspends the memorandum on preventing incidents and ensuring flights safety during operations in Syria signed with the US," the Russian Foreign Ministry said.
Moscow also urged the UN Security Council to hold an emergency meeting to discuss the Syrian situation.
This was the first direct military action President Donald Trump has unleashed against the regime of Syrian President Bashar al-Assad since he took power in January and represents a dramatic escalation in the US military campaign in the volatile region.
Speaking to the media at Florida, the President said Damascus had "ignored the urging of the UN Security Council".
Washington has blamed the Syrian military for the toxic attack of Tuesday in which over 70 persons died in Khan Shaykun town of n Idlib province. Damascus called the allegation a "lie".
Syrian Foreign Minister Walid al-Moallem said the army struck an arms depot of the Al Qaeda-linked Nusra Front and the target contained chemical materials that terrorists had brought from Iraq.
The Syrian airbase hit by the US missiles was used in the war against the Islamic State and played a key role in liberating the ancient city of Palmyra from the jehadist group.
The Russian Defence Ministry said only 23 of the 59 cruise missiles fired from US warships hit the target.
The US said it notified both Russia and Turkey before the missile strike.
"US military planners took precautions to minimise risk to Russian or Syrian personnel located at the airfield," a US statement said, hinting a Russian military presence at the Shairat base.
Russia said it expected the UN Security Council to condemn the US strikes, Russian presidential spokesman Dmitry Peskov said.
Victor Ozerov, the chairman of Russian Federation Council's Committee on Defence and Security, said on Friday that the US strike in Syria was "an act of aggression" against a UN member.
He said it would "undermine the efforts in the fight against terrorism" in Syria and that cooperation between the US and Russia may be "shut down".
In the US, Adam Schiff, the ranking member of the House Intelligence Committee, said there were "no current plans for additional strikes".