The Conservative government announced it is launching a full public inquiry, which will "begin immediately," into the 1985 Air India bombings.

Prime Minister Stephen Harper made the announcement in the House of Commons after question period today.

He said he decided on terms of reference for the inquiry after government officials consulted with some of the families of the 331 victims.

Harper has appointed retired Supreme Court justice John Major to head the inquiry, which will begin immediately.

The prime minister said Justice Major has met with victims' families in Ottawa, Toronto and Vancouver, and has developed detailed terms of reference for the inquiry with "their full support and cooperation."

"And I have every confidence that Justice Major will conduct a thorough, compassionate investigation into the events surrounding this incident."

Major was previously appointed by Harper to recommend guidelines for the inquiry after victims' relatives were consulted.

The bombing of Air India flight 182 killed all 329 people -- more than 80 of them children -- on board in what was the worst terrorist attack and mass murder in Canadian history.

"Canadians and indeed citizens of all countries around the world demanded that those who perpetrated this act be brought to justice. Unfortunately, for a variety of reasons, this has not yet been possible. And we must sadly admit, may never come to pass," said Harper.

"We must never forget that the vast majority of those who perished on Flight 182 were citizens of our country. They were Canadians. They and their families came here just as our ancestors did, to seek a better life for themselves in a country with unlimited opportunity."

Harper said it's our duty, as Canadians, "to do everything in our power to prevent a similar tragedy from ever happening again."

He said although previous governments have launched several inquiries into the tragedy, "for reasons that only they know" they chose not to make them public. He said "families of the victims continue to demand answers that only a full public inquiry can provide."

To accomplish that, said Harper: "A full public inquiry is required. That is what we promise the families, this is what we are announcing today."

The early morning blast on June 23, 1985, sent bodies and debris into the Atlantic Ocean off Ireland as the flight was en route from Toronto to India via London.

A second bomb, which was planted in a suitcase on another Air India flight, killed two baggage handlers when it exploded at Japan's Narita airport.

The bombings ignited deadly riots in Punjab and protests in Vancouver.

Harper has long supported a full judicial inquiry into the tragedy, which the previous Liberal government opposed.

Reporting from Ottawa, CTV's Rosemary Thompson said while she was unsure of the exact details of the inquiry, she said it was likely to be "very expensive."

"The Gomery Inquiry cost upwards of $30 million," she told Newsnet Monday.

"Once you get into these inquiries it costs a lot of money. You've got to go back and find the witnesses and pay for all the lawyers."

Act of vengeance

Crown prosecutors alleged the bombings were an act of vengeance against the government of India following a 1984 raid on the Golden Temple at Amritsar, the holiest shrine for Sikhs.

The raid resulted in the deaths of about 800 Sikhs, including militants taking refuge in the temple.

Indian prime minister Indira Gandhi was assassinated by her Sikh bodyguards in the bloody months following the raid.

Millionaire businessman Ripudaman Singh Malik, of Surrey, B.C., and sawmill worker Ajaib Singh Bagri, of Kamloops, B.C., were acquitted of the bombings in 2005 after a judge ruled that the Crown's case against them was too weak.

Meanwhile, Inderjit Singh Reyat is currently serving a five-year sentence for making the bomb that blew up the flight.

Reyat was sentenced in 2003 after striking a plea bargain under which he was convicted on lesser charges of manslaughter and with assisting in the construction of the bomb.

He was expected to provide testimony in the trials of Malik and Bagri, but later claimed he couldn't remember.

The investigation, which has lasted more than 20 years, has been the costliest in Canadian history at an estimated $130-million.

In November 2005, former Ontario premier and Liberal leadership candidate Bob Rae recommended a focused inquiry be held into both the Air India investigation and prosecution.

With files from the Canadian Press