It’s the latest upheaval in the years-long conflict that now involves several countries and key players. It has prompted responses from around the world, with many leaders promising to take action against the Syrian government suspected to be behind the attack.
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Here’s what to know about the chemical attack, and the response it has gotten.
What exactly happened?
Syrian medical staff, activists and rescue workers all say they witnessed a chemical attack in Douma on Saturday. The town is located in the Eastern Ghouta region, which has been in the news over the past several months as it faces airstrikes and a shortage of basic supplies.
READ MORE: Syrian government accused of chemical attack
Douma, which is home to as many as 150,000 people, experienced two separate bombings that contained “toxic” or “poisonous” gases. That’s according to the Violations Documentation Center (VDC), which monitors and records alleged violations of human rights and international law in Syria.
The VDC said the attacks were carried out by the Syrian Air Force.
Dozens of residents were taken to hospital shortly after. The total death toll is still unconfirmed, but Reuters reports that at least 60 were killed. The World Health Organization said at least 500 people were treated for “symptoms consistent with exposure to toxic chemicals.”
WATCH: What price will Syria pay for its chemical attack?
Who is responsible?
While international leaders squarely lay the blame on the Syrian government, it has repeatedly denied ever carrying out chemical attacks.
Russia, which is known to support the Syrian army, said Wednesday that the United States “invented” reports of the attack.
Both Syria and Russia deny all reports of the chemical attacks.
U.S. President Donald Trump’s reaction — and Russia’s reaction
Meanwhile, U.S. President Donald Trump tweeted Wednesday morning that missiles “will be coming” in response to the attack.
“Russia vows to shoot down any and all missiles fired at Syria,” Trump tweeted. “Get ready Russia, because they will be coming, nice and new and ‘smart!’. You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!”
WATCH: Trump condemns Syria suspected chemical attack
Right after Trump’s tweet, the Russian Foreign Ministry said that U.S. “smart missiles” should be aimed at terrorists, not at the Syrian government.
Trump cancelled a planned trip to Latin America this week in order to mull what action he will take regarding Syria. It’s unclear what he will decide at this point, but he has promised a quick and forceful response.
The attack has also prompted reaction from British Prime Minister Theresa May, who said Wednesday that “the continued use of chemical weapons cannot go unchallenged.”
2013 chemical attack
The latest chemical attack, and the resulting international uproar, resembles what happened in 2013 when Barack Obama was president.
At the time, Syria denied using the chemicals, while Obama promised swift military action.
WATCH: Syrian doctor describes horror he witnessed in chemical attack victims
Obama later decided against intervening in the conflict after Syria agreed to get rid of its chemical weapons.
But a Reuters investigation from August 2017 reported that President Bashar al-Assad’s regime has likely continued to stockpile the weapons.
The investigation found that there have been dozens of sarin gas attacks in Syria since 2013, and they have caused hundreds of deaths.
— With files from Reuters