Two witnesses who were believed to have 'seismic' evidence about the 1985 Air India bombing have refused to testify before the probe panel citing concerns over their personal security while a third one suffered a heart attack hours before he was to take the stand.

Air India Inquiry Commission head Justice John Major said he had hoped to at least hear the testimony of the witnesses in camera on Wednesday before deciding how their evidence could become part of the public record at the inquiry into the terrorist bombings that killed 331.

The witnesses refused to take stand as Major 'could not offer guarantees to the witnesses that their identities would remain secret.'

'The witnesses are apprehensive that the evidence they give which may endanger them or others may be subjected to scrutiny through a variety of means. We cannot assure them of confidentiality. The press has the ability to apply for access to information. There are possibilities of court applications,' Major was quoted by the Vacouver Sun as saying.

The inquiry, which has already heard from 113 witnesses over 44 days, adjourned the hearing until September.

The witnesses would not testify because of the Inquiry Commission could not give them sufficient assurances for their safety, Commission's chief counsel Mark Freiman said.

The commission declined to force their testimony by subpoena because the Commission recognized it could not provide the assurances the witnesses sought that their identities could be kept secret, Freiman was quoted by the Globe and Mail as saying.

Families of the victims said they were distressed by the turn of events because they had been led to believe the witnesses would have important new evidence.

The hearing began with Major suggesting the Commission might convene an in-camera hearing to hear witnesses initially in private. Journalists covering the inquiry objected to it and asked for a delay until they could consult lawyers about the public-interest issue.

Major, who has previously stated that he wants as much of the panel's hearing to be in public as possible, said he would take note the journalists' objections.

Major reconvened the session after a short break and said there would be no hearings of any kind because of the witness-protection issue.

Jacques Shore, a lawyer for Air India bombing victims, said, "I feel like really all the families have been hit in the stomach with something pretty severe because it was our impression that today would be an important day in terms of revealing information potentially evidence that we had never seen before."

Amarjit Bhinder, who lost her pilot husband in the bombing, said she had been looking forward to the evidence.      

"We were very keen to know, very excited in the sense that we were very hopeful that something worthwhile would come out," said Bhinder, who travelled from India to attend the inquiry this week.