The FBI said the Canadian suspects may have had "limited contact" with two men recently arrested on terrorism charges in Georgia. About 400 regional police and federal agents participated in the arrests Friday and early Saturday.

"These individuals were allegedly intent on committing acts of terrorism against their own country and their own people," Prime Minister Stephen Harper said in a statement. "As we have said on many occasions, Canada is not immune to the threat of terrorism."

The Royal Canadian Mounted Police arrested 12 adult suspects, ages 43 to 19, and five suspects younger than 18 on terrorism charges including plotting attacks with explosives on Canadian targets. The suspects were either citizens or residents of Canada and had trained together, police said.

The group acquired three tons of ammonium nitrate - three times the amount used to blow up the Murrah Federal Building on April 19, 1995, in Oklahoma City, killing 168 people and injured more than 800, said assistant Royal Canadian Mounted Police commissioner Mike McDonell.

The fertilizer can be mixed with fuel oil or other ingredients to make a bomb.

"This group posed a real and serious threat," McDonell said. "It had the capacity and intent to carry out these attacks."

Luc Portelance, assistant director of operations with Canada's spy agency, CSIS, said the suspects "appeared to have become adherents of a violent ideology inspired by al-Qaida" but that investigators have yet to prove a link to the terror network.

Five of the suspects were led in handcuffs Saturday to the Ontario Court of Justice, which was surrounded by snipers and bomb-sniffing dogs. A judge told the men not to communicate with one another and set their first bail hearing for Tuesday.

Alvin Chand, a brother of suspect Steven Vikash Chand, said outside the courthouse that his brother was innocent and authorities "just want to show they're doing something."

"He's not a terrorist, come on. He's a Canadian citizen," Chand said. "The people that were arrested are good people, they go to the mosque, they go to school, go to college."

FBI Special Agent Richard Kolko said in Washington there may have been a connection between the Canadian suspects and a Georgia Tech student and another American who had traveled to Canada to meet with Islamic extremists to discuss locations for a terrorist strike.

Syed Haris Ahmed and Ehsanul Islam Sadequee, U.S. citizens who grew up in the Atlanta area, were arrested in March.

Officials at the news conference displayed purported bomb-making materials including a red cell phone wired to what appeared to be an explosives detonator inside a black toolbox. Also shown were a computer hard drive, camouflage uniforms, flashlights and walkie-talkies. A flimsy white door riddled with bullet holes was on display but no details about it were available.

According to a report Saturday in The Toronto Star citing unidentified police sources, the suspects attended a terrorist training camp north of Toronto and had plotted to attack the Canadian spy agency's downtown Toronto office, among other targets in Ontario province. Authorities refused to confirm those reports.

The suspects lived in either Toronto, Canada's financial capital and largest city, or the nearby cities of Mississauga or Kingston.

Also at the court hearing was Aly Hindy, an imam of an Islamic center that houses a school and a mosque and has been monitored by security agencies for years. He said he knows nine of the suspects and that Muslims once again were being falsely accused.

"It's not terrorism. It could be some criminal activity with a few guys, that's all," said Hindy. "We are the ones always accused. Somebody fakes a document and they are an international terrorist forging documents for al-Qaida."

Rocco Galati, lawyer for two suspects from Mississauga, said his client Ahmad Ghany, 21, is a health sciences graduate from McMaster University in Hamilton. He was born in Canada, the son of a medical doctor who emigrated from Trinidad and Tobago.

Shareef Abdelhaleen, 30, is a computer programmer who emigrated from Egypt 20 years ago with his father, now an engineer with a nuclear utilities services company, the lawyer said.

The charges came under Canada's Anti-Terrorism Act, which was passed shortly after the Sept. 11, 2001 attacks - and after Osama bin Laden named Canada as one of five "Christian" nations that should be terror targets. The other countries - the U.S., Britain, Spain and Australia - have all been targeted.

Portelance, of Canada's spy agency, said it was the nation's largest counterterrorism operation since the adoption of the act and that more arrests were possible.

The adult suspects from Toronto are Chand, alias Abdul Shakur, 25; Fahim Ahmad, 21; Jahmaal James, 23; and Asin Mohamed Durrani, 19. Those from Mississauga are Ghany; Abdelhaleen; Zakaria Amara, 20; Asad Ansari, 21; Saad Khalid, 19; and Qayyum Abdul Jamal, 43.

Mohammed Dirie, 22, and Yasim Abdi Mohamed, 24, are from Kingston.