The M.V. Sun Sea entered an economic zone that Canada claims within 200 miles (320 km) of Vancouver Island and was being tracked by a Canadian navy warship that will intercept it as it nears land, officials said.

Officials believe there are between 400 and 500 people on the boat, but the exact number and where they are from will not be known until the ship is boarded by Canadian authorities, said the officials.

The ship would likely be escorted to Victoria, British Columbia, and could arrive there as early as late Thursday or early Friday.

Reports have circulated for weeks that a vessel carrying Tamil migrants fleeing Sri Lanka was headed to Canada. A boat with 76 Tamils seeking refugee status arrived on Canada's Pacific coast in October.

"I can advise you that we have been watching this boat for 2 1/2 months or perhaps even longer, and we have some idea of who is on board," Public Safety Minister Vic Toews told CTV News on Wednesday.

The issue has created a quandary for the Canadian government, which has treaty agreements to protect people fleeing persecution but also wants to prevent large-scale human smuggling of Tamils leaving Sri Lanka.

"Those responsible for migrant smuggling will be pursued, investigated and prosecuted to the full extent of Canadian law and in accordance with the provisions of international conventions and protocols," the Foreign Affairs Department said on Wednesday.

There is also concern that some of those on board may be members of the Tamil Tigers, which fought an independence war against Sri Lankan government forces. Canada considers the group an illegal terrorist organization.

Similar accusations were made about migrants on the ship that arrived on the West Coast last October. All 76 people on board were eventually allowed to make refugee claims in Canada, which are still being processed.

The Canadian Tamil Congress says the people on the Sun Sea are likely civilians fleeing persecution and that the Sri Lankan government claims they are Tamil Tigers to make their refugee claims in Canada more difficult.

"They try to paint them with a bad brush right off the bat," David Poopalapillai, a spokesman for the Tamil group, said in an interview.

Toews would not confirm if the government believes Tamil Tigers are involved with the boat, but hinted it was prepared for the possibility.

"We are quite aware of potential issues that might arise when this boat enters our territorial waters," he said.