A bomb blast at an election rally outside Colombo killed about 50 people Sunday, including the opposition candidate for president and top leaders of his party.
More than 200 people were thought to have been wounded.
The assassination of Gamini Dissanayake came less than three weeks before the election and just before peace talks were to resume with Tamil Tiger guerrillas. The 11-year-old civil war has killed more than 34,000 people.
Dissanayake was an outspoken critic of the talks that began this month, and the government had warned him three weeks ago that the Tigers would try to kill him.
The talks scheduled for today were called off, said government delegate Navin Gunaratne. No new date was set.
The bomb ripped through the rally on the outskirts of Colombo shortly before midnight. Dissanayake had just finished speaking and was stepping off the stage to greet supporters at his last stop of the day, a Defense Ministry spokesman said.
"The bomb was apparently at the front of the stage," said Weerasooriya Wickrema, campaign manager of Dissanayake's United National Party. "It was a very powerful bomb."
There was no immediate claim of responsibility, and police said it was too early to say who might have set the blast. But the Tigers have a long history of assassinations and suicide bombs.
They were blamed for the killing last year of President Ranasinghe Premadasa and of Indian Prime Minister Rajiv Gandhi in May 1991. Dozens of Sri Lankan politicians and military leaders have also been killed by bombs.
An emergency meeting of Prime Minister Chandrika Kumaratunga's Cabinet decided to postpone the Nov. 9 election, in which she was to stand as a candidate for the ruling alliance.
The Tigers have been fighting since 1983 for an independent homeland for the Tamil minority in the north and east. The Tamils comprise about 18 percent of Sri Lanka's 17-million people.