A Sri Lankan minister and senior Tamil political leader on Wednesday escaped unhurt, but one of his aides was killed and a security guard critically injured when a suspected woman Liberation Tigers of Tamil Eelam suicide bomber blew herself up in his office in Colombo.

The bomber, a physically challenged woman, got past one layer of security in the office of social services and social welfare minister Douglas Devananda, but detonated the bomb when she was stopped at the second check post near his room, officials said.

The public relations officer of the minister, Stephen Perras, was wounded and succumbed in a hospital, they said adding, one of Devananda's bodyguards was seriously injured.

Another man working in the office was slightly hurt. The bomber was also killed.

Devananda, the leader of Eelam People's Democratic Party, was inside the office, but escaped unhurt, his brother Dayananda said.

"This was an attempt to kill the minister," said military spokesman Brig Udaya Nanayakkara, blaming the Tamil Tigers. The rebels, however, denied responsibility.

A vocal critic of the LTTE, militant-turned-politician Devananda escaped assassination bids four times in the past. The bomber got past one layer of security in the Minister's office without being checked as she was a polio victim and was allowed on sympathetic grounds, a defence official said.

"It is a public day when the minister tries to redress the grievances and complaints of the people in his office," Dayananda said. Officials also said the woman bomber took advantage of the public day to target the Minister.

A few days earlier, two persons were arrested in Colombo on suspicion of conspiring to kill Devananda. The 50-year-old leader lives in a fortified building and travels in heavy security.

The EPDP, once part of the rebel cause, renounced violence and joined the political mainstream in 1987. Security was beefed up in Colombo following the incident with barricades set up in important junction points, creating a traffic snarl.

The attack comes a day after LTTE supremo V Prabhakaran said peace with the island's 'genocidal' government was impossible and accused it of 'trying to destroy the Tamil nation'.

Delivering the annual Heroes' Day speech on his 53rd birthday, he also vowed that the rebels would strike back after a difficult year, adding that the government was 'over-confident of its military victory over the Tamil freedom movement'.