Among the myriad military and intelligence agencies that make up Iran's security forces, none has the skill and reach of the Quds Force, an elite unit nominally within the command structure of the Iranian Revolutionary Guard Corps.
Like the Revolutionary Guard, the Quds Force and its predecessors were among the semiofficial militias, charities and centers of clerical power born of the paranoia and zeal of the tumultuous years after Iran's 1979 Islamic Revolution, which brought Ayatollah Ruhollah Khomeini to power.
Originally, the Revolutionary Guard played a defensive role. In the 1980s, Iran's Shiite revolutionaries faced a war against Iraq as well as the hostility of Iranian secular nationalists, the West and Sunni-dominated regimes of the Middle East.
The Revolutionary Guard was entrusted to protect Khomeini's theocracy. But the revolutionaries also were inspired to spread their vision abroad.
The Quds Force and its predecessors consisted of the Guard's most skilled warriors. Experts said they were highly secretive commando units sent abroad to help Shiites usurp monarchies in the Persian Gulf, gun down enemies and battle Israeli forces in southern Lebanon. They also reportedly have run operations in Sudan, South Asia and Western Europe.
Their plans sometimes coincided with U.S. interests, as when they supported Afghans fighting the Soviet Union in the 1980s and Bosnian Muslims battling Serbs in the 1990s.
The Quds Force also has been involved in Iraq. It assisted Kurdish rebels fighting Saddam Hussein in the 1980s and Shiites battling his regime in the 1990s. Even Ahmad Chalabi's expatriate Iraqi National Congress had Quds Force help, experts say.
At most, the force numbers 2,000, said Mahan Abedin, director of research at the Center for the Study of Terrorism, a London think tank.
"It's a remarkably efficient organization, quite possibly one of the best special forces units in the world," he said.
The extent to which the Quds Force is controlled by the government has been hotly debated in U.S. foreign policy circles.
"This has been a topic of debate among Iran experts inside and outside the government for 25 years," said Kenneth M. Pollack, an Iran expert at the Brookings Institution's Saban Center for Middle East Policy. "There are people who believe the Quds Force does not move a muscle without getting explicit orders from [supreme leader Ayatollah Ali] Khamenei; there are other people who believe they are rogues. The weight of evidence is somewhere in the middle."
There are signs that Quds Force-linked operatives have taken orders from Tehran for overseas missions.
Most notable, Pollack said, were the 1992 killings of an Iranian Kurdish separatist leader and three associates in Berlin by four gunmen led by an Iranian agent. In 1997, a German court found that the slayings had been ordered by a government committee in Tehran that included Khamenei and then-President Hashemi Rafsanjani.
There has been evidence of rifts between Iran's government and the Revolutionary Guard and Quds Force. The Revolutionary Guard occasionally has tried to push the government into more extremist positions.
In 1998, for example, thousands of Guard troops gathered on the border with Afghanistan in what appeared to be a move against the Taliban regime. There was suspicion that the Revolutionary Guard was working independently. The government later sent conventional forces to "keep a watch" on the Guard, Pollack said.
"We do have evidence here and there, circumstantial in many ways, that the Quds Force guys and other people in the Revolutionary Guard like to push the edge of the envelope," Pollack said, speculating that the Quds Force could be freelancing in Iraq.
"Tehran almost certainly told the Quds Force to go into Iraq," he said. "What we don't know is: Did they say something as vague as, 'Protect our interests in Iraq without actually going to war with the Americans'? Or did they say something very specific: 'Do this, do that, don't do this.'
"We don't know."
Daragahi reported from Baghdad and Spiegel from Washington.
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A look at Iran's military
Iran has two military branches: the armed forces and the specialized Islamic Revolutionary Guard Corps. Each has a navy and air force. The Revolutionary Guard has a special forces unit called the Quds Force, which U.S. officials say is aiding Iraqi militants. Al Quds is the Arabic name for Jerusalem, a city considered holy to Islam. Some U.S. analysts say the two military branches are in competition for resources and influence in the government.
Islamic Republic of Iran Regular Forces
Ground troops: 350,000
Air force: 30,000
Islamic Revolutionary Guard Corps
Ground troops: 100,000
Air force: Unspecified
Quds Force: 2,000
Basij paramilitary force: 2 million
Sources: CIA, Times reporting