The United States, Britain and France launched strikes against the Syrian regime in response to an alleged chemical weapons attack after mulling military action for nearly a week.

A Royal Air Force tornado comes into land in the early hours from RAF Akrotiri airbase in Cyprus after conducting air strikes in Syria. April 14, 2018.
A Royal Air Force tornado comes into land in the early hours from RAF Akrotiri airbase in Cyprus after conducting air strikes in Syria. April 14, 2018. (AFP)

The United States, Britain and France carried out a wave of punitive strikes against Bashar al Assad's Syrian regime on Saturday in response to alleged chemical weapons attacks that US President Donald Trump branded the "crimes of a monster."

As Trump embarked on a White House address to announce the action – taken in defiance of Russia's threat to respond – explosions were heard in the Syrian capital Damascus, signalling a new chapter in a brutal civil war, now in its eighth year.

On April 7 the Syrian American Medical Society (SAMS) and Syria's White Helmets rescue force jointly say more than 40 people died in a "poisonous chlorine gas attack" in Douma, the last opposition-held town in eastern Ghouta near the capital.

Blaming the Syrian regime, they said there are "more than 500 cases" of people with "symptoms indicative of exposure to a chemical agent."

Here are five things you need to know about the attacks.

1: The strikes targeted Syria's chemical weapons programme

The air strikes were aimed at "chemical weapons infrastructure" in what the US billed as a warning against Assad employing such weapons in the future – a warning he has not heeded in the past.

They targeted a scientific research facility in the Damascus area, a chemical weapons storage facility west of the city of Homs and a third location that contained both a command post and a chemical weapons equipment storage facility in the same area, the US military said.

The Syrian Observatory for Human Rights (SOHR) monitoring group said that "scientific research centres" and "several military bases" were hit in the strikes.

France, Britain and the US carried out a wave of pre-dawn strikes against Syria's regime in response to a suspected chemical weapons attack. April 14, 2018.
France, Britain and the US carried out a wave of pre-dawn strikes against Syria's regime in response to a suspected chemical weapons attack. April 14, 2018. (AFP)

2: Naval and air assets were involved

More than 100 cruise missiles were fired, a significant number of which were intercepted by Syrian regime forces, Russia's defence ministry says.

US, British and French "naval and air assets" took part in the strikes, which US defence chief James Mattis said employed more than twice the amount of munitions used in American strikes in Syria last year following the Khan Shaykhun chemical attack. In that assault, the US fired 59 Tomahawk missiles at regime targets.

Britain's defence ministry said that four Tornado jets fired Storm Shadow missiles, while the French defence ministry released video footage of Rafale warplanes taking off to carry out the strikes.

A British military Typhoon aircraft lands at the Sovereign Base Area (SBA) of Akrotiri, a British overseas territory located ten kilometres west of the southern Cypriot port city of Limassol, following US, British and French strikes on Syria. April 14, 2018.
A British military Typhoon aircraft lands at the Sovereign Base Area (SBA) of Akrotiri, a British overseas territory located ten kilometres west of the southern Cypriot port city of Limassol, following US, British and French strikes on Syria. April 14, 2018. (AFP)

3: Reactions have been mixed

Syrian regime media termed the strikes "a flagrant violation of international law" and said the intervention "is doomed to fail," while Syrians crowded onto the streets of Damascus in noisy demonstrations of defiance.

Syria's opposition, on the other hand, said the strikes on regime military positions did not go far enough, casting them as a "farce" as long as Bashar al Assad remains in power. 

The Kremlin condemned the air strikes on Syria where its armed forces are backing Assad and said it was calling an emergency session of the United Nations Security Council, where it is a permanent member, to discuss the "aggressive actions" of the US and its allies.

Iran's supreme leader Ayatollah Ali Khamenei denounced  Trump, France's Emmanuel Macron and Britain's Theresa May, branding them "criminals."

Damascus skies erupt with anti-aircraft fire as the US launches an attack on Syria targeting different parts of the Syrian capital Damascus, Syria, early Saturday, April 14, 2018.
Damascus skies erupt with anti-aircraft fire as the US launches an attack on Syria targeting different parts of the Syrian capital Damascus, Syria, early Saturday, April 14, 2018. (AP)

4: The attack came shortly before a chemical weapons investigation

A team of inspectors from the OPCW arrived in Syria on Thursday and Friday and had been expected to start their investigation into the alleged Douma attack on Saturday.

The OPCW later issued a statement saying the global chemical watchdog's Fact-Finding Mission (FFM) team had arrived in Damascus, to commence its work.

Russia says the strikes were probably designed to prevent investigators from the global chemical weapons watchdog from doing their work.

"It's ... highly likely an attempt to create complications for the Organisation for the Prohibition of Chemical Weapons (OPCW) mission which was just starting its work in Syria's Douma, or an attempt to completely derail it," Interfax quoted the chairman of the international affairs committee of Russia's upper house of parliament, Konstantin Kosachev, as saying.

A suspected chemical attack left hundreds of people struggling with respiratory issues in Douma in Syria's eastern Ghouta, according to the White Helmets. April 7, 2018.
A suspected chemical attack left hundreds of people struggling with respiratory issues in Douma in Syria's eastern Ghouta, according to the White Helmets. April 7, 2018. (SyriaCivilDef / Twitter)

5: There are contradictory claims about last week's attack

France concluded after technical analysis of open sources and "reliable intelligence" that the chemical attack was carried out by Syrian regime forces, a declassified intelligence report showed on Saturday.

Russian Defense Ministry spokesman, Maj. Gen. Igor Konashenkov, said that images of victims of the purported attack were fakes staged with "Britain's direct involvement," without providing evidence.

The accusations followed an earlier statement by Russian Foreign Minister Sergey Lavrov, who said that "intelligence agencies of a state that is now striving to spearhead a Russo-phobic campaign were involved in that fabrication." 

The Britain-based SOHR did not confirm Douma had been hit with a chemical attack. It reported, however, at least 70 cases of respiratory difficulties among civilians after regime air strikes, initially saying 11 people had died. That number later rose to at least 40.

The Syrian regime has a history of using chemical weapons. UN human rights investigators, have documented 34 chemical weapons attacks in Syria since 2013, including 26 which they attribute to regime forces, the most recent one on the Harasta frontline in eastern Ghouta in November 2017. The perpetrators of the remaining six have not been identified.