In a statement, the Liberation Tigers of Tamil Eelam called Prabhakaran an "incomparable leader" who had "attained martyrdom," BBC reported Sunday
The group said it has declared a week of mourning starting Monday, the British network reported.
The statement said Prabhakaran was killed "fighting the military oppression of the Sri Lankan government" last Sunday.
The Tamil rebels made a last stand after Sri Lankan troops cornered them in a coastal strip. The loss marked at least a temporary end to the 26-year fight for a separate Tamil homeland.
The BBC reported that a spokesman for the group said it would now use non-violent methods to fight for Tamils' rights.