- Moscow and Tehran have warned that there would be consequences for the US-led attacks on Syria.
Russian President Vladimir Putin has denounced a strike on Syria launched by the US and its allies as an "act of aggression" that will exacerbate humanitarian catastrophe in Syria.
In a statement issued by the Kremlin, the Russian leader says Moscow is calling an emergency meeting of the United Nations' Security Council over the strike launched by the US, Britain and France.
Putin added that the strike had a "destructive influence on the entire system of international relations".
He reaffirmed Russia's view that a purported chemical attack in the Syrian town of Douma that prompted the strike was a fake.
Putin added that Russian military experts who inspected Douma found no trace of the attack.
He criticised the US and its allies for launching the strike without waiting for inspectors from the international chemical weapons watchdog to visit the area.
US President Donald Trump ordered the air attacks late on Friday "on targets associated with chemical weapons capabilities".
Russia's ambassador to the US warned that there would be consequences for the attacks.
"A pre-designed scenario is being implemented," Russian Ambassador Anatoly Antonov said on Twitter.
"Again, we are being threatened. We warned that such actions will not be left without consequences."
Antov added that it was not acceptable to insult Russia's president: "Insulting the President of Russia is unacceptable and inadmissible."
"The US - the possessor of the biggest arsenal of chemical weapons - has no moral right to blame other countries."
Later on Saturday, the Syrian presidency posted a video that appeared to show President Bashar al-Assad arriving for work hours after the strike.
"The morning of resilience," declared a caption accompanying the video circulated on the presidency's Telegram feed.
"The barbaric aggression ... will not affect in any way the determination and insistence of the Syrian people and their heroic armed forces," state news agency SANA cited an official source in the Syrian foreign ministry as saying.
WATCH: Russia warns of 'consequences' after US-led strikes in Syria (1:17)
"This aggression will only lead to inflaming tensions in the world" and threatens international security, the source added.
Iran also warned of "regional consequences" following the attacks.
"The United States and its allies have no proof and, without even waiting for the Organisation for the Prohibition of Chemical Weapons to take a position, have carried out this military attack... and are responsible for the regional consequences," said foreign ministry spokesman Bahram Ghasemi on his Telegram channel.
A senior official in a regional alliance that backs Damascus said the Syrian government absorbed the attacks, adding that the targeted sites were evacuated days ago thanks to a warning from Russia.
"We had an early warning of the strike from the Russians ... and all military bases were evacuated a few days ago," the official said.
Around 30 missiles were fired in the attack, and a third of them were shot down, the official added.
"We are carrying out an assessment of the material damages," the official added.
President Assad has been backed in the seven-year-long Syrian war by Russia, Iran, and Iran-backed groups, including Lebanon's Hezbollah.
Explosions were heard in Damascus, Homs and elsewhere in Syria.
A US official told Reuters news agency the attacks were aimed at multiple targets and involved Tomahawk cruise missiles.