Justin Trudeau. REUTERS/Chris Wattie

President Donald Trump called Canadian prime minister Justin Trudeau on Monday to offer condolences over a shooting at a Quebec City mosque on Sunday night that left six dead.

"President Trump expressed his condolences to the Prime Minister and people of Canada following the tragic shooting at the Centre culturel islamique de Québec, located in Québec City, and offered to provide any assistance as needed," Trudeau's office said in a statement, according to The Toronto Star.

White House press secretary Sean Spicer confirmed the call between the two leaders Monday.

Trudeau further said that Muslim-Canadians are an "important part" of Canada's "national fabric," according to a statement.

"These senseless acts have no place in our communities, cities and country," Trudeau said.

The sole suspect, a French-Canadian university student named Alexandre Bissonnette, was in police custody as of Monday morning.

Two suspects were initially apprehended following the shooting. However, police now believe that the second person, Mohamed Belkhadir, was a witness who called 911.

"They consider this a lone wolf situation," a source familiar with the matter told Reuters.