MISSISSAUGA, Ontario - An Islamic center, where some of Canada's 17 Muslims arrested recently on terror charges have prayed, was closed and silent on Monday as the Muslim community reacted with shock to the news.

A sign on the door of the al-Rahman Islamic Center for Islamic Education said prayers were at 1:45 p.m. but the center was mostly deserted, with only a throng of media gathered outside.

"I was shocked, it (the alleged criminal element) should not be here. This is a religious place," said the owner of a nearby store, who said he attended the mosque about once a week.

A massive anti-terror sweep over the last several days led to the arrest of the 17 men and youths, who are accused of planning to build huge bombs and blow up landmark locations in southern Ontario.

The group's high-profile targets included the Peace Tower in Ottawa's Parliament Buildings and Toronto's CN Tower, according to media reports on Monday.

Court documents summarized on the Toronto Star website on Monday show that 12 men - a publication ban prohibits identifying the five who are youths aged below 18 - face charges ranging from "conspiracy to carry out a terrorist activity, to training for terrorist purposes, to bombmaking and illegally importing guns and ammunition."

Several of the accused have attended the mosque, and a local parliamentarian has complained in the past about radical views held by some of its worshipers.

Canada's Council on American-Islamic Relations put out a statement expressing relief that the arrests had averted "potential terror attacks."

But other Islamic groups feared a backlash against Muslims, who make up an estimated 2 per cent of Canada's population of 33 million.

Vandals smashed windows at a Toronto area mosque on Saturday night.

Canada's spy agency said the anti-terror sweep meant there was no longer an "imminent threat", but police couldn't rule out further arrests in what is already the country's largest counter-terrorism operation.

The group had the "intent and capability" to launch attacks, Mike McDonell, assistant commissioner of the Royal Canadian Mounted Police, told CBC Radio on Monday.

"There is a chance we could be arresting more people. We are following up every lead to the Nth degree, and any person that has aided, facilitated or participated in this threat will be arrested."

The men and youths were arrested on Friday and Saturday in an operation that involved some 400 police officers in and around Toronto, Canada's largest city and its economic powerhouse.

All of those arrested were residents of Canada, and most were citizens, prompting parallels to be drawn with the London bombings of a year ago, when young British suicide bombers killed 52 people and wounded 700 by setting off bombs on the city's transit system.

Canada's spy agency said the arrests meant it "would be irresponsible to say that there is an imminent threat just as it would be irresponsible to say that there's no threat."

A spokeswoman for the Canadian Security intelligence Service added: "We've been living in an elevated threat environment since 9/11 and that elevated threat environment continues."

Charges against the 17 include participating in, or contributing to, a terrorist group, as well possessing firearms and explosives.

Police said the group had amassed three metric tons of ammonium nitrate, a fertilizer that can be mixed with fuel oil to create a powerful explosive. That's three times the amount of ammonium nitrate used in the Oklahoma City bombing of 1995, which killed 168 people.

"Obviously anybody who's collecting three tonnes of ammonium nitrate isn't doing it for purposes of fertilizing their gardens," Public Safety Minister Stockwell Day told CTV Television on Sunday. "There was very serious intent here."

The Toronto Star newspaper said the group had received the fertilizer as part of a police sting operation, but the RCMP's McDonell said he couldn't confirm this.