COLOMBO, Jan 5: A suicide bomber set off explosives strapped to her body killing herself and 12 others outside Sri Lankan prime minister's office today in the third assassination bid in as many weeks, police said, report agencies.

The woman, believed to be a member of the separatist Liberation Tigers of Tamil Eelam (LTTE), carried out the attack as she was about to be searched by Prime Minister Sirimavo Bandaranaike's security staff, police said.

Just two hours later, a prominent ethnic Tamil political leader, known to be sympathetic to the Tigers, was assassinated in another part of the capital Colombo. He was shot dead at the wheel of his Mercedes Benz.

Gunmen on two motorcycles fatally shot pro-rebel Tamil politician Kumar Ponnambalam, as he was driving in a Tamil neighbourhood. Ponnambalam, 60, had run for president in 1982 and often represented Tamils in human rights cases against the government.

Neither police nor party officials would comment for the record on a possible motive for Ponnambalam's killing.

But assistant police SL Munidasa said officers were searching for a man who had been with Ponnambalam, and disappeared after the shooting, along with the victim's mobile phone and wristwatch.

Police said the true target of the suicide bombing, which was heard in most parts of the city, could have been a senior minister rather than the 83-year-old Prime Minister Bandaranaike who was not due to attend office.

However, senior members of the government used the Flower Road opposite the Prime Minister's office to travel to President Chandrika Kumaratunga's tightly-guarded Temple Trees residence for the weekly cabinet meeting.

The blast went off just 20 minutes before the scheduled cabinet meeting that is held less than a kilometre away. "The woman was seen loitering along Flower Road when alert staff of the prime minister's security division spotted her and tried to question her," a police spokesman said.

"She blasted herself as she was about to be searched."

Six members of the premier's protection staff were among those killed, police and doctors said. Some of those wounded were waiting outside the Russian embassy which shares a boundary wall with the prime minister's office.

No senior officials were killed.

The explosion damaged the outer walls of the building housing the office of Bandaranaike, mother of president Kumaratunga. Earlier police said the blast occurred outside the house, which is nearby.

A dismembered leg lay 30 feet away from the blast site. Four bodies were found at one place, covered with sheet brought from the prime minister's office. Two other bodies were about 40 feet away from the other bodies.

Pieces of human flesh and blood were found all over the place.

"I saw the police people trying to search her," said Nimal Sirisena, a security guard at the Russian embassy, said of the suspected bomber. "She was resisting it and moments later, I heard a big bang," said Sirisena, wiping drops of blood that fell on him.

Sri Lanka's junior defence minister Anuruddha Ratwatte, who is believed to a prime target for Tamil Tiger rebels, also has a state bungalow at the top of Flower Road. Local residents earlier expressed fears that his presence in the area could attract Tiger bombings.

Ratwatte is the hands-on director of the government's military campaign against the Tigers in the island's north-east.

President Kumaratunga herself escaped an assassination attempt last month during the presidential race. A suicide bomber set off explosives strapped to her body as Kumaratunga was getting into her car. She was injured in the right eye and doctors reportedly have said she may lose sight. That blast, at an election rally in downtown Colombo last month also left 26 people dead and more than 100 wounded.