Mr Rigi is said to be behind a series of deadly bombings in south-east Iran
Iranian state television has broadcast a statement by a captured Sunni rebel leader in which he alleges he received support from the United States.
It is not possible to say whether Abdolmalek Rigi made the statement freely or under duress.
The US has denied having links with Mr Rigi's group, Jundullah.
In the tape, Mr Rigi alleged that the US had promised to provide his group with military equipment and a base in Afghanistan, near the Iranian border.
He says he was on his way to a meeting with a "high-ranking person" at the Manas US military base in Kyrgyzstan when he was captured.
Jundullah has launched several deadly attacks in recent years in the south-east of Iran in protest at the discrimination of Sunni minorities in Iran.
The attacks include the killing of six senior commanders of Iran's elite Revolutionary Guard in October.
The taped statement was aired on Iran's state-run English-language channel, Press TV.
ABDOLMALEK RIGI & JUNDULLAH
Leader of Jundullah believed to be 26 years old
The Sunni Baluchi nationalist group emerged 2003
Accused by 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 six 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
In it, Mr Rigi said the initial US contact was made after US President Barack Obama was elected in November 2008 and took place through a person in Quetta, Pakistan.
"The Americans said... that we don't have a problem with al-Qaeda or the Taliban, but the problem is Iran and we don't have a military programme against Iran."
The rebel leader claimed that he was promised US support to launch attacks on Iran in return for the release of Jundullah prisoners.
"They [Americans] promised to help us and they said that they would co-operate with us, free our prisoners and would give us [Jundullah] military equipment, bombs, machine guns, and they would give us a base," he alleged, in translated comments provided by the Press TV.
Predominantly Shia Iran has linked Jundullah to the Sunni Islamist al-Qaeda network and accuses Pakistan, Britain and the US of backing the group to destabilise the country. They deny the accusation.
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 is necessary to draw attention to discrimination.