The first attack by the suicide unit was in March when they targeted the Chief Inspector of an anti-terrorism unit. The officer escaped with injuries.The report quoted defence sources as saying the LTTE hit-squad was targeting President Kumaratunga, three ministers in her cabinet, military chiefs and a legislator from Thiruchelvam's Tamil United Liberation Front (TULF).

Thiruchelvam was warned by security services four days before his death that he was a target, but he reportedly told police he did not think the rebels would use a suicide bomber against him.

The attack against Thiruchelvam, whocontributed to a radical devolution plan which the Tigers opposed, came despite a police alert for a suicide bombers issued two weeks ago.

At the time police said the LTTE had sent a 25-year-old woman along with three others to stage an attack here. LTTE suicide cadres are known as Black Tigers.

``Police also warn the public to be on alert for any suspects as the LTTE hierarchy has ordered its cadres to create havoc in the metropolitan area to mark the Black July,'' a government statement said.

Troops and police have been on alert for Tamil rebel attacks during the whole of July, when the guerrillas celebrate two major anniversaries.The LTTE carried out their first suicide bombing against security forces 12 years ago on July 5, and the Tamil conflict also escalated with anti-Tamil riots in July 1983.

The guerrillas are fighting for a Tamil homeland in the North and East of Sri Lanka. More than 55,000 people have been killed in fighting in the past 27 years.