MISSISSAUGA, Ontario — Several members of a suspected terrorist ring prayed daily at a storefront mosque in a middle-class city west of Toronto but never spoke of hurting others, one of their prayer leaders said.

"I will say that they were steadfast, religious people. There's no doubt about it. But here we always preach peace and moderation," Qamrul Khanson, an imam at the one-room Al-Rahman Islamic Center for Islamic Education, said Sunday.

The 40 to 50 Muslim families that worship at the mosque were astonished, he said, to learn that police had arrested 12 adults, ages 19 to 43, and five suspects younger than 18 on Friday and Saturday, charging them with plotting an attack in southern Ontario. Two Americans who met with the suspects also are in custody.

The group acquired three tons of ammonium nitrate from undercover Royal Canadian Mounted Police officers in a sting operation, the Toronto Star has reported. The fertilizer can be mixed with fuel oil or other ingredients to make a bomb.

That is three times the amount used in the 1995 Oklahoma City bombing, said assistant Royal Canadian Mounted Police commissioner Mike McDonell.

The Toronto Star reported that the investigation began in 2004 with the monitoring of Internet chat rooms.

The 17 suspects represent a spectrum of Canadian society, from the unemployed to a school bus driver to the college-educated. The 12 adults live in Toronto, Mississauga and Kingston, Ontario.

Police said the suspects, all citizens or residents of Canada, had trained together.

"For various reasons, they appeared to have become adherents of a violent ideology inspired by al-Qaida," Luc Portelance, the assistant director of operations with CSIS — Canada's spy agency, said Saturday.

The modest mosque is sandwiched between The Cafe Khan, which offers Pakistani kabobs, and a convenience store in Mississauga, a city of 700,000 people with many immigrants. Mohammed Jan works at the cafe and said several suspects often came in for snacks after prayers.

"It's pretty shocking. They used to come every day and they just seemed normal," Jan said.

Jerry Tavares of Brazil lives two doors down from Jamal's home. He said Jamal was unfriendly and rarely interacted with the neighbors.

"I wasn't surprised," the construction worker said, adding that he intends to move.