A Pakistani tribal militant group responsible for a series of deadly guerrilla raids inside Iran has been secretly encouraged and advised by American officials since 2005, US and Pakistani intelligence sources told ABC News reporters Brian Ross and Christopher Isham.
The group, called Jundullah, is made up of members of the Baluchi tribe and operates out of the Balochistan province in Pakistan, just across the border from Iran.
The group has taken responsibility for the deaths and kidnappings of more than a dozen Iranian soldiers and officials.
US officials said US relationship with Jundullah is arranged so that US provides no funding to the group, which would require an official presidential order or "finding" as well as Congressional oversight.
Tribal sources told ABC News that money for Jundullah is funneled to its youthful leader, Abd el Malik Regi, through Iranian exiles who have connections with European and Gulf states.
Jundullah has produced its own videos showing Iranian soldiers and border guards it says it has captured and brought back to Pakistan.
The leader, Regi, claims to have personally executed some of the Iranians.
"He used to fight with the Taliban. He's part drug smuggler, part Taliban, part Sunni activist," said Alexis Debat, a senior fellow on counterterrorism at the Nixon Center and an ABC News consultant who recently met with Pakistani officials and tribal members.
"Regi is essentially commanding a force of several hundred guerrilla fighters that stage attacks across the border into Iran on Iranian military officers, Iranian intelligence officers, kidnapping them and executing them on camera," Debat said.
Most recently, Jundullah took credit for an attack in February that killed at least 11 members of the Iranian Revolutionary Guard riding on a bus in Zahedan, Iran.
Last month, Iranian state television broadcast what it said were confessions by those responsible for the bus attack.
They reportedly admitted to being members of Jundullah and said they had been trained for the mission at a secret location in Pakistan.
The Iranian TV broadcast is interspersed with the logo of the CIA, which the broadcast blamed for the plot.
A CIA spokesperson said "the account of alleged CIA action is false" and reiterated that US provides no funding of the Jundullah group.
Pakistani government sources say the secret campaign against Iran by Jundullah was on the agenda when Vice President Dick Cheney met with Pakistani President Pervez Musharraf in February.
A senior US government official said groups such as Jundullah have been helpful in tracking Al Qaeda figures and that it was appropriate for the US to deal with such groups in that context.
Some former CIA officers said the arrangement is reminiscent of how the US government used proxy armies, funded by other countries including Saudi Arabia, to destabilise the government of Nicaragua in the 1980s.