OTTAWA?Prime Minister Stephen Harper told a group of new citizens that human smuggling risks undermining support for Canada's "generous" refugee program, according to a transcript out Wednesday.

Ottawa is "concerned" about the "growing problem of mass arrivals through human smuggling," Harper said at a citizenship ceremony held late Tuesday.

In many cases, asylum seekers such as the hundreds who have arrived in the past year on Canada's Pacific coast aboard rickety cargo ships, are seeking to "jump the queue and work around the system," Harper said.

Their actions "call into question the most basic obligation of a sovereign country to control its own borders."

"A failure to act and act strongly, will inevitably lead to a massive collapse in public support for our immigration system," he concluded, promising legislation to curb illegal immigration.

Canada's immigration and public safety ministers are to unveil the legislation on Thursday, government officials said.

Canada, which has a population of around 34 million, accepts an average of 250,000 legal immigrants each year.

Border officials detained 492 illegal Tamil immigrants from Sri Lanka who arrived in August aboard the MV Sun Sea, a leaky cargo vessel. Another 76 were arrested in October 2009 upon arrival on Canada's west coast aboard another battered freighter.

Canada and Sri Lanka allege that there may be members of the Tamil Tigers ? a group Canada considers a terrorist organization ? hiding among the migrants.

After a lengthy civil war, the Tamils were defeated by the Sri Lankan government in 2009.

More ships carrying Tamil asylum seekers are also reportedly en route for Canadian shores, local media reported.

"Not only do we have relatively speaking the largest immigration program in the world; not only do we have the most generous system of sanctuary for refugees in the world ? we also have a level of public support for immigration that is unparalleled elsewhere in the world," Harper said.

"And that must continue, because our economy will need even more immigrants."

During the current session of Parliament "strong new laws" will be proposed aimed at curbing human smuggling and providing incentives for would-be immigrants to enter the country through "legitimate channels," Harper said.