The new head of the defeated Tamil Tiger separatist group was being interrogated in Sri Lanka on Thursday, having been flown to Colombo following his capture in Thailand, reports said.
Selvarasa Pathmanathan, better known as K P, was brought back to Sri Lanka on Thursday and was being questioned at an undisclosed location, the privately run Island newspaper said.
The state-run Rupavahini television channel said he had been arrested in Thailand, but gave no further details.
In a statement posted on its website, the Sri Lankan defence ministry said Pathmanathan had been "taken into custody by Sri Lankan law enforcement authorities."
Pathmanathan, an overseas-based leader who took over the Liberation Tigers of Tamil Eelam (LTTE) following the killing of its supreme leader, Velupillai Prabhakaran, in mid-May, was also wanted by Interpol on gun-running charges.
Two years ago, Pathmanathan had reportedly given the slip to Thai police as he was about to be arrested.
Pathmanathan was appointed international representative of the Tigers during the LTTE's last stand against Sri Lankan security forces who finally routed the rebel group in May, ending one of Asia's longest-running ethnic conflicts.
He later announced that he had taken up the overall LTTE leadership following the death of Prabhakaran who had headed the separatist group since 1972.