The Canadian navy ship HMCS Toronto has seized six tonnes of hashish after stopping and boarding a vessel in the Arabian Sea last week, the Department of National Defence says.

The May 30 seizure came on the heels of four major drug interceptions by HMCS Toronto this spring, including half a tonne of heroin on March 29 and shipments of 317 and 200 kilos of heroin discovered earlier in May.

Based in Halifax, HMCS Toronto has been in the area since January, as part of an international maritime force patrolling the Persian Gulf and Indian Ocean in the wake of the Sept. 11, 2001, attacks.

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The six tonnes of cannabis resin are the largest hashish seizure in the history of the combined maritime forces.

DND did not provide details of the operation but past seizures typically involved spotting suspected sailing vessels (called dhows), sometimes with the help of Sea King helicopters, sending a boarding party and searching the ship for several hours. The narcotics are then destroyed with explosives.

Images released by the Royal Canadian Navy of the May 30 intercept show a party of armed sailors, clad in bulletproof vests and helmets, using a rigid-hull inflatable boat to approach the dhow and get on board.

According to the UN Office on Drugs and Crime, Afghanistan is not only the world's biggest producer of opium but has also become a major producer of cannabis. Western military officials say that maritime seizures such as those conducted by HMCS Toronto are counter-terrorism successes because they disrupt the smuggling of illicit drugs out of Afghanistan, which terrorist organisations use for financial support.

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"Their efforts represent Canada's continuing dedication toward ensuring a secure maritime environment for legitimate mariners in the region," Defence Minister Peter MacKay said in a communiqué.

The task force says that, in accordance with international law, military ships can board and search vessels that are was found to be without nationality.