“We share the view of our allies, I think based on the evidence before us, that there have been uses of chemical weapons in Syria by the regime,” Harper said at a news conference in Paris on Friday.
“The position of Canada on the regime is clear. We want to see Assad depart power and we want to see a regime that’s representative of the entire population of Syria, which the Assad regime in its present form can never be.”
Harper is on a European tour ahead of the G8 summit in Northern Ireland.
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His remarks came after the United States announced it has proof Assad’s forces used chemical weapons — including the nerve agent, sarin — against Syrian rebels.
The U.S. now plans to begin arming the rebels, although precisely how that will be done is not yet clear.
Harper said he still has concerns about the risks of providing weapons and ammunition to the Syrian rebels.
French President Francois Hollande, speaking alongside Harper, said the Syrian opposition must be clear about how it intends to use the weapons.
Hollande also said military pressure must be exerted on Assad’s regime, a sentiment shared by some NATO allies.
"The White House has confirmed what France knew already, that is there are some chemical weapons and they have been used," he said. "We must exert pressure on the regime of Bashar Assad. We must get him to understand that there is no other solution than a political solution. ... Assad must go."
Syria says U.S. announcement 'full of lies'
On Friday, British Foreign Secretary William Hague welcomed the U.S. announcement on chemical weapons, issuing a statement calling for "a strong, determined and co-ordinated response from the international community" on the Syrian civil war.
"We have to be prepared to do more to save lives, to pressure the Assad regime to negotiate seriously, to prevent the growth of extremism and terrorism, and to stop the regime using chemical weapons against its people," Hague said, adding that Britain will be "urgently" discussing the matter at the G8 summit on Monday.
The Syrian Foreign Ministry released a statement Friday describing the U.S. announcement as "full of lies ... based on fabricated information.
"The United States is using cheap tactics to justify President Barack Obama's decision to arm the Syrian opposition," the statement said.
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Russia, an ally of Syria and member of the G8, has resisted calling for Assad to step down. Russian President Vladimir Putin's foreign affairs adviser, Yuri Ushakov, has said the evidence Russia has seen on Assad's use of chemical weapons "didn't look convincing."
At least 93,000 people have been killed in Syria's civil war, according to the latest estimate from the United Nations' human rights office, which noted that the true number of deaths could be much higher.
Syrian forces, aided by fighters from Lebanon's Iran-backed militant group Hezbollah, captured the strategically important town of Qusair on June 5, dealing a heavy blow to rebels who had held the area for more than a year.
Regime troops have since focused on retaking other areas in the central Homs province, and Aleppo to the north.
Hezbollah's leader said Friday the group will continue to fight in Syria "wherever needed." Sheik Hassan Nasrallah said he had made a "calculated" decision to defend Syria and is ready to bear all consequences.