Prime Minister Stephen Harper recently met with members of the Air India Victims Families Association in his office on Parliament Hill in Ottawa. (Chris Wattie/Reuters)

Prime Minister Stephen Harper will mark the 25th anniversary of the Air India bombing by saying "we are sorry" to families of the victims.

"Some wounds are too deep to be healed even by the remedy of time," Harper will say on Wednesday at a memorial service in Toronto in a speech he wrote himself. "We are sorry."

An excerpt from the speech was obtained by CBC News.

Harper will say the destruction of Air India Flight 182 "was, and remains, the single worst act of terrorism in Canadian history."

He will describe terrorism as "an enemy with a thousand faces, and a hatred that festers in the darkest spots of the human mind."

"This was evil, perpetrated by cowards. Despicable, senseless and vicious," Harper will say.

The prime minister will discuss compensation, but will not mention an amount.

Harper's apology follows a scathing report released last week by former Supreme Court justice John C. Major. He blamed a "cascading series of errors" by government, the RCMP and the country's spy agency for failing to prevent the disaster.

Harper called the report a "damning indictment of many things that occurred before and after the tragedy" which the government is "determined to avoid in the future."

The prime minister said the government takes Major's report "very seriously" and will "respond positively" to his recommendations for an apology and compensation for families.

Threat has not vanished: Rae

Flight 182 went down in the Atlantic Ocean near Ireland on June 23, 1985, killing all 329 people aboard, most of them Canadians. A separate luggage bomb destined for a second Air India flight killed two Japanese baggage handlers at Tokyo's Narita airport.

In 2005, Bob Rae, now a Liberal MP, led a fact-finding mission into the bombing on behalf of the federal government. He said the threat is still not over, and Canadians must remain vigilant.

"I think that hatred and complacency are both responsible for what happened in Air India and I think that there's still a risk that those two emotions are still too much alive in our country," Rae said.

Major's inquiry into the bombing — how it occurred, why the authorities failed to find those responsible and whether it could happen again — began on June 21, 2006.

Inderjit Singh Reyat was the only person ever convicted in the case. He pleaded guilty to manslaughter in 2003.

Suspected ringleader Talwinder Singh Parmar died in India in 1991, and the RCMP's two main surviving suspects — Ripudaman Singh Malik and Ajaib Singh Bagri — were both acquitted in March 2005 after a 19-month trial. B.C. Supreme Court Justice Ian Josephson ruled that the Crown's case against the two was too weak for a conviction.

Ceremonies to mark the bombing of Air India flight 182 will be held across the country today, including in Vancouver's Stanley Park.

Treasury Board President Stockwell Day will attend that ceremony organized by family members at the Air India Memorial at Ceperley Playground at 7 p.m. PT.