The 12 men, aged between 19 and 43, and five teenagers younger than 18, all had Arabic names and were nearly all Canadian citizens.

They were arrested during raids on Friday night in Toronto. Police said that they found three tonnes of ammonium nitrate and a mobile phone that had been modified to become a detonator.

The amount of explosive was three times the amount of ammonium nitrate used in the Oklahoma City bombing in 1995, which destroyed a federal building, killing 168 and injuring more than 800.

The police refused to divulge the terror suspects’ alleged targets, but a report in the Toronto Star said that the group had been focusing on the parliament buildings in Ottawa and the offices of the Canadian Security Intelligence Services in Toronto.

The police said that the men had attended a training camp together and had made videotapes of their activities. They also said that they had had contact with two terror suspects arrested in the US in March. Since the 7/7 bombings in London, Canadian authorities have given warning of the potential for the country’s own strain of homegrown Islamic extremism, especially with the presence of Canadian troops in Afghanistan.

In Toronto’s suburbs, there are growing Muslim communities and an increasing number of mosques. Last night, vandals smashed 30 windows of one Toronto mosque and damaged nearby cars.

Luc Portelance, assistant director of operations with the Canadian intelligence services, said that the suspects “appeared to have become adherents of a violent ideology inspired by al-Qaeda”.

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