NEW DELHI, MAY 1 -- President Ranasinghe Premadasa of Sri Lanka was assassinated today by a suicide bomber who strapped explosives to his body and rammed his bicycle into the presidential party during a May Day parade in the island nation's capital.

Premadasa and at least 11 other people, reportedly including the police commissioner along with presidential bodyguards, died in the blast, which turned the festive rally in the country off India's southeast coast into a scene of carnage. At least 60 people were injured in the explosion, police said.

The assassination threw Sri Lanka, already enmeshed in a 10-year-old civil war, into political chaos and likely will provoke a bitter power struggle to fill the vacuum. The insurgency by ethnic Tamils, mainly Hindus, seeking a separate state in the north and east has killed 17,000 of Sri Lanka's 17 million people, 75 percent of whom are Sinhalese and mostly Buddhist.

No group claimed responsibility for the assassination, although speculation focused immediately on the rebel Liberation Tigers of Tamil Eelam, who were accused of sending the suicide bomber who killed Indian prime minister Rajiv Gandhi two years ago. The Tamil rebels denied responsibility for Premadasa's assassination, the British Broadcasting Corp. reported from Colombo, the capital.

Suspicion also centered on an opposition political party seeking revenge for the April 23 assassination of Premadasa's chief political rival, Lalith Athulathmudali. The government blamed his death on the Tamil Tigers, but Athulathmudali's followers blamed Premadasa for the killing by a lone gunman at an election rally.

Prime Minister Dingiri Banda Wijetunge, 71, was sworn in as interim president several hours after the noontime explosion. Under Sri Lanka's constitution, the parliament must elect a new president by secret ballot within a month. Premadasa, 68, who also occupied the post of defense minister, had groomed no obvious successor.

His death occurred as Sri Lanka was beginning to rebuild its war-ravaged economy. Before the separatist movement paralyzed the country, Sri Lanka was viewed by many economists as a potential rival to the economic centers of Southeast Asia. Premadasa was credited by many for returning some financial stability to the country.

{In a statement in Washington, President Clinton praised Premadasa as having "worked tirelessly to promote his country's development and raise the standard of living of all Sri Lankans." His assassination was "a brutal act of terrorism" that left him "outraged," Clinton said.}

"It has been a terrible shock to the entire country," Neelan Tiruchelvan, a lawyer who heads a Sri Lankan political think tank, said in a telephone interview from Colombo. "Two of the leaders of the three main political parties have been assassinated within the last week. It creates a further crisis in terms of political succession."

The blast occurred as the president was leading a May Day march of blue-collar workers down Colombo's main thoroughfare to a seaside esplanade in the heart of the city at about 12:45 p.m. Premadasa's United National Party had organized the parade.

Bystanders spotted a man riding a bicycle emerge from the crowd and pedal toward the president's entourage, Tiruchelvan said witnesses reported. The suicide bomber was knocked against a vehicle and an explosion ripped through the crowd, he said.

The military later said the suspected bomber was believed to be a teenager, possibly as young as 14, news agencies reported.

Evans Cooray, the president's spokesman, told reporters that he had left the president's side moments before the blast to answer a telephone call. "I looked around and saw some people thrown in the air," he said.

Cooray said the president, wearing white clothes and a green cap, had just jumped off a jeep and was standing in the road "signaling to some senior ministers who were coming along in the procession" when the bomb exploded.

The place was "full of blood and pieces of flesh," television cameraman Sydney Chandrasekhara told a reporter at the scene. Cooray said the scene "was like a battlefield." Police said the blast blew off the bomber's head, and that wires were found attached to his clothing. The street was littered with the shoes of thousands of bystanders who fled the explosion.

For 30 minutes, the whereabouts of the president was unknown, Cooray said. "We thought he had been taken away by security people, but later his body was reported to be lying in the police morgue."

The government did not announce the president's death until 6 p.m. -- five hours after the blast -- when the state television network played a tape of a BBC report of the assassination, according to Tiruchelvan, who watched the telecast.

The government placed the island under curfew tonight. In some areas, celebrations over the president's death were reported.

Premadasa was elected in 1988 in the midst of the insurgency by the Tiger separatists in the north and east as well as Sinhalese rebels in the south. He failed in attempts to negotiate a peace with either group.

Premadasa, who was born in the slums and educated by Buddhist monks, rose to political power to become a champion for the oppressed, building thousands of model homes for the poor and handing out loans to the underprivileged. Last year, he launched a project to set up 200 garment factories in the countryside.

Opponents criticized those actions as gimmicks to win votes and some of his own party members, led by Athulathmudali, launched an unsuccessful effort to impeach Premadasa in 1991.