Iranian TV pictures showed Mr Rigi being escorted from a plane
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 semi-official Fars news agency, quoting the Iranian intelligence ministry, said the arrest took place of the "Jundullah leader along with two of his group members".
ABDOLMALEK RIGI & JUNDULLAH
Leader of Jundullah believed to be
Baluchi nationalist group emerged 2003
Iran of links with the US and Pakistan
Thought to be linked to
drug smugglers in Iranian border province of Sistan-Baluchistan
Brother Abdolhamid Rigi on death row in Iran
October 2009 a Jundullah suicide bomb kills 31, including 6 top Revolutionary Guard commanders
May 2009 bomb in a mosque in the provincial capital Zahedan kills 19
April 2007 Mr Rigi appears on Voice of America radio
February 2007 a bomb kills 11, including Iranian Revolutionary Guards, in Zahedan
March 2006 gun attack kills 22
Sources: BBC, Stratfor
The official IRNA news agency later said he had been flying 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.
The group has been using neighbouring Pakistan as a base, and in the past the Iranians have accused Pakistan of allowing them to operate there.
Mr Rigi has claimed in the past that the group does not seek to break away from Iran but that violence is necessary to draw attention to discrimination.