The government of Canada is backing U.S. president Donald Trump's first use of military force.

Yesterday, the U.S. fired Tomahawk cruise missiles on a Syrian air base. 

Earlier this week, Syrian government planes took off from this location and reportedly dropped chemical weapons against its own civilians in a rebel-held area near the Turkish border.

“Canada fully supports the United States’ limited and focused action to degrade the Assad regime’s ability to launch chemical weapons attacks against innocent civilians, including many children," Canadian prime minister Justin Trudeau said in a statement. "President Assad’s use of chemical weapons and the crimes the Syrian regime has committed against its own people cannot be ignored. These gruesome attacks cannot be permitted to continue with impunity."

Trudeau also called the Syrian air attacks "a war crime", noting that "Canada condemns all uses of chemical weapons."

“Canada will continue to support diplomatic efforts to resolve the crisis in Syria,” the prime minister said.

Meanwhile, one of Syria's strongest allies, the Russian government, has called the U.S. air strikes a war crime, saying they were made under a "false pretext".

Russia has suspended military cooperation with the U.S in Syria.

Syrian president Bashar al-Assad has claimed that the attacks came after "propaganda" was released falsely claiming he had used chemical weapons.

And Syrian ally Iran has insisted there's no proof that chemical weapons were used and that the U.S. military action will support terrorists.

The Nuremburg Tribunal following the Second World War described a war of aggression as the "supreme international crime".

Under international law, it's legal to wage war in self-defence or with the support of the UN Security Council, but it's illegal for one country to unilaterally launch a war of aggression against another state.

In a statement last night, Trump invoked the concept of self-defence in justifying the U.S. government's use cruise missiles.

The president said that there is "no dispute" that Syria used chemical weapons, which are banned, violating its legal obligations under the chemical weapons convention.

"Years of previous attempts at changing Assad's behaviour have all failed and failed very dramatically," Trump said. "As a result, the refugee crisis continues to deepen and the region continues to destabilize, threatening the United States and its allies."