The Canberra bomb was defused by police after it was detected by an X-ray machine.
Police believe both bombs were sent by the same person.
Police and postal authorities fear more bombs could be in the mail.
The Brisbane bomb went off in a room only 40 metres from Mr. Bjelke-Petersen’s office, hurling wire shrapnel at two postal clerks.
Four hours later a second letter bomb with similar stencil typewriting on the envelope arrived at a Canberra building where Mr. Fraser plans to set up his office.
Both envelopes were marked “Press Release Kit.”
Police experts think the author may be a foreigner because of the shape of some of the lettering.
The Brisbane bomb was posted on Tuesday night in Drummoyne, a Sydney suburb. Mr. Fraser’s bomb was posted in the neighbouring suburb of Five Dock about the same time.
The Australia Police’s Assistant Commissioner for Crime, Mr. J. D. Davies, warned last night that there was no way of knowing whether other bombs had been posted.
The incidents triggered a national police alert over security for political leaders during the election campaign, and brought a $20,000 reward offer from the Australian Postal Commission.
Mr. Fraser said last night there was now a clear obligation on Australian political leaders to use “language that does not unduly inflame passions” during the election campaign.
“Extremist language has been used in recent days and every Australian will know in their own minds, in their own hears, who has used extreme language,” he said.
He said the letter bomb attempt was one of several threats on his life over the past six weeks – but he would not allow them to interfere with his election campaign.
Mr. Whitlam said tactics of violence and extremism must be resisted.
“I condemn absolutely any form of violence in our political life,” he said.
The bomb addressed to Mr. Bjelke-Petersen exploded in the faces of two clerks on the 14th floor of the Government executive building in George Street, Brisbane.
One of the clerks, Mr. Keith McFarlane, 24, had a piece of metal removed from his right eye in a three-hour operation at the Princess Alexandra Hospital late yesterday.
Doctors said last night it was too early to tell if Mr. McFarlane would lose the use of his eye.
The other clerk, Mr. Gary Kross, 34, is in a satisfactory condition with face, chest and stomach injuries in Royal Brisbane Hospital.
Mr. Bjelke-Petersen was in an RAAF plane bound for Mackay when the bomb went off.
When he was told of the blast he said: “How horrible. It is deplorable that two innocent officers have been injured.”
“But despite this and other threats of intimidation I will carry on with my job with all my might.”
Police explosive experts said last night both bombs were basically the same – very powerful, very dangerous and built to kill or seriously maim anyone within five metres of the detonation.
“It’s a plastic explosive used commercially to cut steel and sheet metal or by farmers to blow out trees,” one expert said.
“The idea of the letter bomb is simple enough for a 12-year-old child.”
The letter bomb addressed to Mr. Bjelke-Petersen was picked up in mail batch from the Brisbane GPO at 8:45 am yesterday.
A spokesman for police headquarters in Brisbane said: “We’re treating it as an assassination attempt. If the Premier had opened it himself he would have had his face blown off.”
The spokesman said the two clerks became suspicious of the envelope and put it aside after unsealing it.
It exploded soon after, blowing a hole in the sorting table.
The Canberra bomb was discovered by a security officer in the mail office of the Prime Minister’s Department after a regular afternoon delivery.
Mr. Davies said last night the office put the letter aside when he became suspicious of its contents. It was later examined under a fluoroscope – like an X-ray machine – at police headquarters.
“It was found to contain a quantity of explosives,” he said. “It took our people about half an hour to defuse it.”
Police said the Canberra letter was addressed to “The Minister, Mr. Fraser, MP, Qest Bloc, Queen Victoria Terrace, Parkes, A.C.T.”
Below this was written “Press Release Kit”.
The address is the main office of the Prime Minister’s but is some distance from Mr. Fraser’s personal office in Parliament House.
Government security officials are believed to check about 10 suspicious packages addressed to Government departments and Parliamentarians each day.
It is believed that all departments were alerted so that in future, particularly during election campaigns, security measures will be intensified.
Police last night asked newspapers and TV stations to run photos of both the Brisbane and Canberra letters in the hope that the distinctive handwriting on each would be recognised.
The Postmaster-General, Mr. Nixon, said last night he has ordered the Postal Commission to investigate “practical steps” to help overcome the letter bomb problem.
“I have also asked the commission to seek information from Britain on any steps that may have been taken to handle a similar problem there,” he said.
Mr. Fraser said the letter bomb incidents were deplorable acts and would shock decent people everywhere.
“I call on all Australians to avoid political extremism,” he said. “It has not in the past been part of Australia’s political life.”
Mr. Fraser said a campaign had been launched to inflame the emotions of the electorate – but the Liberal Party and the National Country Party would not be a part of it.