Gunmen attacked a suburban Quebec City mosque as worshipers were finishing their prayers Sunday night, killing six and wounding at least eight, reports Washington Post.

A spokeswoman for the Sûreté du Québec, the Quebec provincial police, said that two suspects had been arrested who remained unidentified. Authorities do not believe at this time that others were directly involved in the attack at the Quebec Islamic Cultural Center.

Police provided no possible motive as they launched their investigation. But government officials wasted no time calling it an act of terrorism.

“We condemn this terrorist attack on Muslims in a centre of worship and refuge,” Canadian Prime Minister Justin Trudeau said in a statement.

“While authorities are still investigating and details continue to be confirmed, it is heart-wrenching to see such senseless violence,” he added. “Diversity is our strength, and religious tolerance is a value that we, as Canadians, hold dear.”

Quebec Premier Philippe Couillard called the shooting a “terrorist act,” saying at an overnight news conference that he reacted with “horror and incredulity” when he learned about the attack. He promised increased police protection for mosques and Islamic centers across the province of Quebec.

“We are with you,” Couillard said, addressing the province’s Muslim community. “You are at home. You are Quebecois.”

While mosques in Canada and the United States have been the targets of numerous acts of vandalism and other hate crimes in recent years, the Quebec City attack appears to be the first mass shooting at an Islamic house of worship in North America.

One of the suspects was arrested 14 miles east of the mosque along the shore of the St. Lawrence River on the approach to a bridge leading to the Island of Orleans. The bridge was closed by authorities. The second suspect was arrested close to the mosque, according to police.

Witnesses said at least two gunmen in hoods or ski masks opened fire on congregants at the Quebec Islamic Cultural Center. Police said the six people killed were between 35 and 70 years old. In addition to the eight injured worshipers, a further 39 people escaped without injury, indicating that there were 53 people at the mosque when the gunmen hit. Authorities did not provide information on the type of firearms used in the shooting.