The alleged role played by the Revolutionary Guard's shadowy, elite Qods force in helping the Taliban, and the extent to which the Iranian leadership may be involved, has been hotly debated within the Pentagon and the U.S. intelligence community.
In a confidential assessment of the war, the top U.S. and NATO commander in Afghanistan, Army General Stanley McChrystal, said Iranian military assistance was not an immediate threat to Western forces but could become one in the future.
A counterterrorism official, speaking on condition of anonymity, said the degree of Qods assistance — supplying arms and providing training to Taliban elements — had reached "very troubling" proportions, underscoring heightened concerns within the intelligence community.
The CIA and other agencies have been stepping up their presence in Afghanistan, deploying more officers to accommodate a surge in demand for intelligence on the Taliban and other threats, a U.S. intelligence official said.
Two years ago, the Bush administration dubbed the Revolutionary Guard a proliferator of weapons of mass destruction and imposed sanctions on its Qods force.
It accused the group of arming and training militants in Iraq who, in turn, attacked U.S. forces.
Pentagon officials pointed to the seizure late last month in western Afghanistan, near the border with Iran, of weapons and explosives bearing markings indicating they were made in Iran.
The large weapons cache, the first seized in Afghanistan in nearly two years, included rockets, explosives, improvised explosive devices (IEDs), as well as munitions known as explosively formed penetrators, or EFPs, capable of piercing U.S. armor, Pentagon officials said.
U.S. officials said they believed the Iranian government was aware of the assistance but it was not clear to what extent its leaders were directly involved.
US SAYS IRAN PLAYING BOTH SIDES
Mainly Shi'ite Iran has historically played a complicated role in Afghanistan.
Tehran was a foe of the Taliban when the hardline Sunni movement ruled Afghanistan.
Since the group's ouster in a U.S.-backed invasion in 2001, Tehran has provided developmental assistance and political support to the government of Afghan President Hamid Karzai.
U.S. officials said Iran appeared to be trying to play both sides, currying Taliban favor in case they return to power while trying to undercut the American military and enhance its bargaining power in talks over its nuclear program.
Set up after the 1979 Islamic revolution to protect the ruling system against internal and external threats, the Revolutionary Guard has about 125,000 members and is the most important wing of Iran's military.
Qods, which means Jerusalem, is the guard's special operations unit, handling activities abroad.
In his assessment of the war, a copy of which was obtained by the Washington Post and posted online, McChrystal said the Qods force was "reportedly" training fighters for certain Taliban groups and providing other forms of military assistance to insurgents.
"Iran's current policies and actions do not pose a short-term threat to the mission, but Iran has the capability to threaten the mission in the future," McChrystal wrote.
Pentagon officials said the presence of Iranian-made improvised explosive devices in the recently discovered cache in Afghanistan was particularly troubling because those weapons cause the highest number of Western casualties. (Reporting by Adam Entous; Editing by Simon Denyer and Cynthia Osterman)
