Amal Jayasinghe from the news agency AFP: "The Government seems to be trying hard"

The leader of the military wing of the People's Liberation Organisation of Tamil Eelam, N Manikkadasan, was killed instantly in the explosion, in the northern town of Vavuniya, 140 miles (220km) north-east of the capital, Colombo.

Two other people were also killed.

Last year, Mr Manikkadasan contested local elections and was elected a council member, but failed to become the mayor of Jaffna.

He has been accused of human rights of violations and of using violence against rivals as well as civilians.

Landmine attack

Police said Mr Manikkadasan had been killed by a suicide bomber, but later reports say the blast was caused by a landmine.

The blast happened at Lucky House, the organisation's headquarters in Vavuniya.

The People's Liberation Organisation of Tamil Eelam accused the Tamil Tigers rebel movement of being behind the bombing.

A leader of the group, Dharmalingam Sidharthan, said the Tigers carried out the attack with the use of a claymore mine planted at Lucky House.

A BBC correspondent says if the attack was a result of an inside job, it would raise more questions of infiltrations within Tamil groups cooperating with the Sri Lankan government.

Last week, the human rights group, Amnesty International, called on the Tigers to stop targeting moderate politicians.

In a statement issued in Colombo, Amnesty said several Tamil politicians had received threatening letters and phone calls, and were at immediate risk of assassination.