Velupillai Prabhakaran, who led a ruthless struggle for nearly three decades for a separate Tamil Eelam in Sri Lanka, was killed in last week's final battle in the northern region, the LTTE admitted for the first time on Sunday.
LTTE's international relations head Selvarasa Pathmanathan told BBC in an interview that their 'incomparable leader attained martydom'.
The Sri Lankan Army had on Monday last said it has killed the rebel leader when he tried to flee in an ambulance.
A day later, troops recovered his body near a lagoon in the 'No Fire Zone' in the Wanni region. However, Pathmanathan said 54-year-old Prabhakaran died on Sunday last, but did not give details of the circumstances that led to his death.
In its 30-year-struggle for a separate state for Tamils in Sri Lanka, the LTTE decimated a number of Sri Lankan Tamil and Sinhalese leaders and former Indian Prime Minister Rajiv Gandhi.
In a statement signed by Pathmanathan, the rebels said they had declared a week of mourning for their dead leader, starting Monday, it reported.
The statement calls on Tamils all over the world to 'restrain from harmful acts to themselves or anyone else in this hour of extreme grief'.
Pathmanthan said the Tigers would now use 'non-violent' methods to fight for the rights of Tamils. Sri Lankan Army had on Saturday said that they have cremated Prabhakaran's body.
Started in 1972 as Tamil New Tigers by a group of young boys headed by Prabhakaran and renamed as Liberation Tigers of Tamil Eelam in 1975, the outfit became more aggressive after the infamous Wellikade jail massacre in which separatists leaders Kuttimani and Jagan were eliminated by the forces.
Though the LTTE occasionally paused for diplomacy, first initiated by India in Thimpu in 1985 and later by Norway in 2002, there was no looking back for the dreaded organisation from its chosen path of gun.
Prabhakaran led the LTTE from secret jungle locations in Wanni in northern Sri Lanka and survived many a battle but the current assault from the Lankan forces ended his dream as well as his life.