Agents with Israel's spy agency, Mossad, have posed as CIA agents in operations to recruit members of the Pakistani group Jundallah, according to a report in US-based Foreign Policy magazine.
Using US dollars and passports, the agents passed themselves off as members of the US Central Intelligence Agency in the operations, according to memos from 2007 and 2008, said the report which was published on Friday.
It is unclear whether the recruitment programme is ongoing.
"Israel has done this before. I know of a report very widely accepted in the US of Israeli Mossad agents in the United States, actually recruiting American Muslims," Mark Perry, who authored the report, told Al Jazeera.
"I think that there is a general conspiracy theory that we work very closely with Israel, that we're willing to forgive [Israel] ... I don't think that's the case here.
"The United States has been very impatient with these kinds of activities and we won't be tolerant of them."
He also warned of the potential vulnerabilities caused by this kind of secret actions.
"If the Iranians believe that we are behind these kinds of activities, then they can target our scientists or Americans overseas and we certainly don't want an ally of ours putting our citizens at risk."
Jundallah [which translates to "soldiers of God"] says it is fighting for the interests of Iran's southeastern Sistan-Baluchistan province's large ethnic Baluch community, whose members, unlike most Iranians, mainly follow the Sunni branch of Islam.
The Baluch straddle the border with neighbouring Pakistan and Afghanistan and Jundallah fighters have taken advantage of the unrest in the region to find safe haven in the border area.
According to the US government, the group is responsible for targeting Iranian government officials and killing Iranian women and children, Foreign Policy said.
In July it claimed responsibility for attacking the Grand Mosque in Sistan-Baluchistan capital of Zahedan, reportedly targeting members of Iran's elite Revolutionary Guards Corps, killing 28 people.
Mossad 'didn't give a damn'
"It's amazing what the Israelis thought they could get away with," a US intelligence officer told Foreign Policy.
"Their recruitment activities were nearly in the open. They apparently didn't give a damn what we thought," said the official.
The memos were written during the last years of then-president George Bush's administration. The former US president "went absolutely ballistic" when briefed on the memos, Foreign Policy said.
"The report sparked White House concerns that Israel's programme was putting Americans at risk," an officer told the magazine.
"There's no question that the US has co-operated with Israel in intelligence-gathering operations against the Iranians, but this was different.
"No matter what anyone thinks, we're not in the business of assassinating Iranian officials or killing Iranian civilians," said the official.
The Mossad activities could further jeopardise the already tense relationship of the US with Pakistan, which is an official ally in the fight against al-Qaeda, which had been pressed to take action against Jundallah, said Foreign Policy.
Tensions in the US-Iran relationship have also spiked, most recently following the car-bombing of an Iranian nuclear scientist.
Foreign Policy, however, said there was no evidence of a link between the scientist's killing and Jundallah.