CANADIAN security officials have boarded a cargo ship carrying hundreds of suspected Tamil asylum-seekers from Sri Lanka dissuaded by Australia.

Public Safety Minister Vic Toews said yesterday that 490 were onboard and that the Thai-flagged vessel MV Sun Sea had declared them to be refugees.

The ship is believed to have headed across the Pacific after the Gillard government toughened its stance on asylum-seekers. The MV Sun Sea approached Australia but was either turned away or feared it would not be allowed to dock.

Mr Toews said the government had concerns there may be members of the rebel Liberation Tigers of Tamil Eelam on board. Canada has labelled the Tamil Tigers a terrorist group since 2006.

Mr Toews’s office originally issued a statement yesterday saying the navy had boarded the ship, but a government official corrected that to say the ship was not boarded until shortly after 9pm eastern Canadian time (1200 AEST Friday).

The government official said the ship was boarded by navy, police and border services officials and was being taken to a navy base on Vancouver Island near the provincial capital, Victoria.

The cargo ship, which had been tracked for days by Canadian and US authorities, was intercepted on Thursday after it appeared to veer from its expected destination in the Vancouver area, authorities said.

Mr Toews said some of the people on the ship were suspected people-smugglers and terrorists.

He pledged that Canada would prosecute anyone involved in human trafficking, which he denounced as a “despicable crime”.

“While our government believes in offering protection to genuine refugees, it is imperative that we prevent supporters and members of a criminal or terrorist organisation from abusing Canada’s refugee system,” Mr Toews said.

Chitranganee Wagiswara, Sri Lanka’s high commissioner to Canada, has said Canada should not accept the Tamils’ claims for refugee status and said the ship was part of a people-smuggling operation linked to the Tamil Tigers.