It is the biggest intervention by Western powers against Assad in Syria’s seven-year civil war, and has pitted the US and its allies against Moscow.
Here’s what we know so far about the strikes.
Who and why?
The strikes were conducted by the US, the UK and France following a suspected chemical attack on the town of Douma, which left an estimated 70 people dead.
In a televised address from the White House, US President Donald Trump said: "A short time ago, I ordered the United States Armed Forces to launch precision strikes on targets associated with the chemical weapons capabilities of Syrian dictator Bashar al-Assad."
“A combined operation with the armed forces of France and the United Kingdom is now under way. We thank them both. This massacre was a significant escalation in a pattern of chemical weapons used by that very terrible regime.”
He said the mission was to “establish a strong deterrent against the production, spread, and use of chemical weapons,”as he criticised Iran and Russia for supporting Assad.
UK Prime Minister Theresa May said the strikes were not about "regime change," but "about a limited and targeted strike that does not further escalate tensions in the region and that does everything possible to prevent civilian casualties."
She said it sent a message to anyone who used chemical weapons, and came after efforts to use diplomatic channels were “repeatedly thwarted.”
“Even this week the Russians vetoed a Resolution at the UN Security Council which would have established an independent investigation into the Douma attack. So there is no practicable alternative to the use of force to degrade and deter the use of chemical weapons by the Syrian Regime.”
French President Emmanuel Macron said France had joined the US and UK because “we cannot tolerate the recurring use of chemical weapons, which is an immediate danger for the Syrian people and our collective security.”
"The red line set by France in May 2017 has been crossed," he said.
US Defence Secretary James Mattis and Marine General Joseph Dunford said three main chemical weapons facilities were targeted at 9 pm EST (2 am CEST) by missiles from both the sea and aircraft.
The strikes targeted:
- A scientific research facility in Damascus, allegedly connected to the production chemical and biological weapons
- A chemical weapons storage facility west of Homs
- A chemical weapons equipment storage and an important command post, also near Homs
In total, the US and its allies fired more than 100 missiles, but the Pentagon could not confirm how many hit their targets.
The Pentagon said the strike was designed to degrade Syria's chemical weapons capability without killing civilians or foreign fighters.
"We specifically identified these targets to mitigate the risk of Russian forces being involved," Dunford told reporters.
Mattis said the joint strikes against Syria were a "one-time shot" unless Assad continues to use chemical weapons.
A senior official in the regional alliance that has supported Assad in the Syrian war told Reuters the attack on Syria will be seen as limited if it is now over and there is no second round.
Syrian and Russian response
Syrian state TV described the strikes as a “flagrant violation” of international law. It said air defenses confronted the attack and had shot down 13 missiles in the Kiswah area south of Damascus.
Russia’s Defence Ministry issued a statement saying that more than 100 cruise missiles and air-to-land missiles were fired by the US, Britain, and France from the sea and air “at Syrian military and civilian targets”.
The statement said “a significant number” of missiles were shot down by Syrian air defences.
Russia’s ambassador to the US warned that there would be consequences for the strike.
“The worst apprehensions have come true. Our warnings have been left unheard...We warned that such actions will not be left without consequences,” Ambassador Anatoly Antonov said in a statement.
“All responsibility for them rests with Washington, London and Paris. 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.”
Russia's Foreign Ministry described the strikes as an "outrageous violation" of international law.”
Iran’s Foreign Ministry strongly condemned the airstrikes and warned of its regional consequences.
Canadian President Justin Trudeau said the country supports the decision “to take action to degrade the Assad regime's ability to launch chemical weapons attacks against its own people.”
"We will continue to work with our international partners to further investigate the use of chemical weapons in Syria. Those responsible must be brought to justice," he said.
Israel commended the swift response of the US and its allies.
"Last year, President Trump made clear that the use of chemical weapons crosses a red line. Tonight, under American leadership, the United States, France and the United Kingdom enforced that line.
“Syria continues to engage in and provide a base for murderous actions, including those of Iran, that put its territory, its forces and its leadership at risk," an Israeli official told NBC News.
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