Iranian authorities have arrested the leader of the Sunni Muslim militant group Jundullah, according to reports on state television.
The Arabic language channel al-Alam said Abdolmalek Rigi had been held in eastern Iran, but gave no more details.
He is said to be behind a series of deadly bombings and killings in Sistan-Baluchistan province.
Last October 42 people, including six Revolutionary Guard commanders, were killed in a suicide bombing in Zahedan.
The Fars news agency, quoting the Iranian intelligence ministry, said the arrest took place of the "Jundullah leader along with two of his group members".
The official IRNA news agency later said he had been travelling in a plane to an Arab country via Pakistan before his arrest.
"His plane was ordered to land and then he was arrested after the plane was searched," Iranian lawmaker Mohammed Dehgan was quoted by news agency AFP as saying.
Press TV, the Iranian state-run English language service, said Mr Rigi had been in a US military base 24 hours before his capture.
It alleged the US had issued Mr Rigi with an Afghan passport.
It also said he had recently travelled to "European countries".
None of these claims could be independently verified.
Jundullah was founded in 2002 to defend the Baluchi minority in the poor, remote and lawless region of south-east Iran.
Mr Rigi has claimed in the past that the group does not seek to break away from Iran but that violence isnecessary to draw attention to discrimination.