UK police and immigration services have arrested a prominent Sri Lankan rebel figure and placed him in immigration detention, British officials say.
Col Karuna used to be one of the Tigers' best commanders
No details were given of where Vinayagamoorthi Muralitharan, better known as Colonel Karuna, was detained or what would happen to him.
Col Karuna has been leading a faction of the Tamil Tiger rebels since splitting from the main group in 2004.
He is said to have later collaborated with Sri Lankan government forces.
Col Karuna was arrested following a joint operation between Britain's new Border and Immigration Agency and London police, a UK Home Office statement said.
"He is now being held in immigration detention [and] it would not be appropriate to comment further," it added.
The Tigers control large swathes of northern Sri Lanka where they run a de facto state.
But the 2004 split is widely seen as having contributed to rebel defeats in the east.
Col Karuna says he left the rebel movement because disproportionate numbers of cadres from the east, like him, were being sacrificed on the battlefield, while the rebels from the north controlled the organisation.
As rebel chief in the east he commanded several thousand fighters, but analysts say his forces now number only a few hundred at most.
The Tamil Tigers have always accused the government of providing shelter to him.
Col Karuna and the authorities deny this.