Ottawa: Canada is not immune to the threat of terrorism and so \"continued vigilance is essential\", Prime Minister Stephen Harper has said.

Harper made the remarks on Tuesday while laying a wreath in the Hall of Honour to mark the \"National day of Remembrance for Victims of Terrorism\" observed to honour those killed in the 1985 Air India bombing.

An Air India flight flying from Toronto to London crashed off the coast of Ireland on June 23, 1985, killing all 329 people on board. Most of the dead were Canadians of Indian origin.

Sikh extremists were blamed for the bombing.

Harper said he cannot \"help but cast his mind back to the Canadians who perished in Air India Flight 182 and in the World Trade Centre attacks... and to the many terrorist activities foiled by the vigilance of Canadian security agencies.

\"The recollections serve as a reminder that Canada is not immune to the threat of terrorism and that continued vigilance is essential.\"

Addressing a gathering in parliament building here, he said it was a terror attack that killed the 329 passengers and crew members aboard Air India.

\"On this sombre anniversary, we stand in solidarity with the friends and families who lost loved ones in that heinous attack and honour those lost.

\"We were deeply moved by this solemn tribute as well as by our meeting the kin of the victims,\" he added.

Among the kin of the victims present was Susheel Gupta, whose mother Ramvati died in the bombing. Gupta said he regretted that his children would not be able to meet their grandmother.

Meanwhile, a memorial service in Ireland was attended by India\'s Minister of State for External Affairs V.K. Singh, Irish Minister for Foreign Affairs Charlie Flanagan and Canadian Minister of Justice Peter MacKay.

Canada must guard against terrorism: PM