With formal charges released for the adult suspects in a massive terror investigation, the RCMP hinted more arrests could be coming.

Details about the case are beginning to emerge just days after 15 suspected Islamic terrorists were taken into custody following the delivery of three tonnes of what they believed to be ammonium nitrate.

Mike McDonell, the assistant RCMP commissioner on the investigation, was if more people could be taken into custody.

"I think that's fair to say, yes, that they will," McDonell told CTV.

"We're following every investigative lead that we have right now. And anybody that was involved in aiding, facilitating or participating in this terrorist threat will be arrested," he said, adding, "we are not done by any stretch of the imagination."

In an interview with U.S. National Public Radio, McDonell said the probe had expanded beyond Canada.

"We are working with and sharing our information with our allied countries," he said.

Intelligence officers are investigating ties between the 17 suspects and Islamist terror cells in the United States and five other countries.

According to an Associated Press story, those countries include Britain, Bangladesh, Bosnia, Denmark and Sweden.

Shortly after the chemicals were delivered, the raids in Toronto and Mississauga began Friday, and into the early morning hours Saturday.

Twelve men were arrested, along with five male teenagers whose identity is shielded under the Youth Criminal Justice Act.

All 12 of the men are facing one count each of participating in a terrorist group.

Three of those men -- Fahim Ahmad, Mohammed Dirie, and Yasin Abdi Mohamed -- also face charges of importing weapons and ammunition for the purpose of terrorist activity.

Nine of the men are charged with receiving training from a terrorist group, while four of them are charged with providing training.

Six are also charged with intending to cause an explosion causing serious bodily harm or death.

Fifteen of the 17 accused appeared in a Brampton court on Saturday, and are due to return on Tuesday for a bail hearing.

Two of the accused are already in jail in the Kingston., Ont., area serving two-year prison terms for trying to smuggle handguns across the Peace Bridge at Fort Erie, Ont.

Some of the alleged evidence includes fatigues, computers and an apparent cellphone-based bomb detonator.

Police are also investigating a property near Washago, Ont., located in the cottage country north of Toronto.

CTV Toronto reported that neighbors of the property recall hearing bursts of automatic gunfire.

Groups of men would go camping there every other week, they said.

Targets

As for targets, police have only said they were in southern Ontario. However, McDonell assured the public that Toronto's transit system was never in harm's way.

"There have been numerous threats and incidents involved around the TTC in the last couple of weeks, and just to put people at ease, we gave that information up," said McDonell.

Public Safety Minister Stockwell Day told Mike Duffy Live that fertilizer bombs were generally delivered by truck, which would rule out Toronto's subway system.

"This would have been directed towards public buildings," he said.

A report in Monday's Globe and Mail says the Peace Tower and Parliament buildings in Ottawa were among the alleged terror targets.

The downtown offices of the Canadian Security Intelligence Service, the CN Tower and Toronto Stock Exchange were also the focus of an alleged bomb plot, the newspaper says.

McDonell wouldn't say how long the investigation went on before the raids were carried out a few days ago in Toronto and Mississauga.

"It was a very complex and intensive investigation with well over 400 resources involved in it, (and) thousands of hours of work."

White House reacts

White House Press Secretary Tony Snow applauded the efforts of the Canadian authorities, saying he felt "relief" at the arrests.

"We're very happy that there's been some successful co-operation, it's an international effort... not only relief but we congratulate Canadian authorities on intercepting such a plot," Snow told reporters at a briefing in Washington on Monday.

But the arrests have also sparked renewed charges from south of the border that Canada has become a safe harbour for terrorists because immigration laws are too lenient.

Snow refrained from saying whether he was concerned about so-called lax immigration policies and refugee asylum policies.

"I'm not going to get into characterizing al Qaeda penetration in Canada ... U.S. and Canadian authorities have been pretty vigorous in working the intelligence on this," Snow said.

"As you know this has become a hot political issue in Canada but far be it for me to get involved in internal Canadian politics," he said.

Indeed, the topic came up in question period on Tuesday when Liberal Leader Bill Graham asked the prime minister what actions Ottawa is taking to respond to "inaccurate attacks on immigration policies."

Prime Minister Stephen Harper conceded that the matter came up briefly when he spoke to some American governors last week and promised to counter fallacious allegations.

"Let me just say I know also that our minister have been in touch with our colleagues in the United States. The American administration has been very co-operative," Harper said.

"The American media generally has covered the story accurately. We will deal with the inaccuracies that are being perpetrated in some circles," he said.

While the White House praised Canada's response, authorities bolstered security at all U.S. points of entry since the arrests happened. Both U.S. and Canadian officials fear suspects might try to enter the U.S.

Monitoring chat rooms

A report in the Toronto Star says CSIS began monitoring an Internet chat room in fall of 2004 after a group of disaffected youths began espousing anti-Western views.

The RCMP was brought into the case on Nov. 17, 2004, by CSIS after the agency thought it had enough information to warrant a criminal investigation, says the Star.

"My experience tells me they would have wire taps on these guys -- all of their cellphones, all their Internet, bugs in the cars bugs in their houses," said former undercover RCMP operative Chris Mathers.

This winter, Ontario's police forces and Toronto Mayor David Miller were alerted to the investigation as intelligence analysts began to get more and more concerned about the group.

The raids took place after the RCMP intercepted the group's order for fertilizer, and arranged to have it delivered by truck, says the Star.

Before delivering the fertilizer, police switched it with a harmless powder, the newspaper says.

Ammonium nitrate

Ammonium nitrate is a common fertilizer found in many hardware, gardening and farm supply stores. However, when mixed with with fuel oil, it can make a powerful bomb.

Terrorism expert Alan Bell said it's not difficult to manufacture this type of bomb.

"It's not a sophisticated type of weapon to be able to put together, and you can get the information on the Internet as most people are doing today," he said.

Ammonium nitrate has a long and infamous history. The Irish Republican Army used it for over 25 years. In 1995, white supremacist Timothy McVeigh used one tonne of ammonium nitrate to blow up Oklahoma City's Alfred P. Murrah building. The blast killed 168 people.

Militants used ammonium nitrate in the 1993 bombing of the World Trade Center in 1993, and the 2002 bombing of a Bali nightclub that killed 202 people.

"Obviously it's a concern and it's being looked at," Public Safety Minister Stockwell Day said.

Because of its lethal properties, the Canadian Fertilizer Institute has been keeping a record of purchases, especially unusually large orders.

The industry said it expects new federal regulations in the fall.

With reports from CTV's Denelle Balfour, Robert Fife and files from The Associated Press