KABUL (Reuters) - As Afghanistan moves centre-stage in U.S. foreign policy, the new administration will need more than a troop surge to defeat the Taliban and bring peace: it will also have to engage Iran, its long-time foe sitting in the wings.
President Barack Obama's administration is conducting a full policy review on Iran which is expected to include Tehran's role in Afghanistan, while the head of NATO, which leads some 55,000 troops in Afghanistan, said dialogue with Iran was crucial to fighting the insurgency there.
"It is absolutely essential, you cannot stabilise Afghanistan without Iran," said Ahmed Rashid, author of a widely acclaimed book on the Taliban.
Germany, the third largest troop contributor in Afghanistan, has also joined the chorus of diplomatic voices for dialogue with Iran, suggesting recently a "contact group" of nations to kick-start rapprochement.
With the U.S. planning to deploy up 30,000 extra troops to Afghanistan in the next 12 to 18 months, and faced with supply-line challenges over insecure routes from Pakistan, the need for wider regional cooperation is acute and urgent.
"Pakistan has only been partially helpful in fighting al Qaeda and the Taliban ... talking to Iran will put a lot more pressure on Pakistan and neighbouring countries to cooperate with NATO and American forces in Afghanistan," Rashid said.
When asked whether any future talks with Tehran might touch on Afghanistan, U.S. State Department spokesman Robert Wood said there needed to be a regional approach to Afghanistan and that included Iran last week.
Alternative routes to Afghanistan for U.S. and NATO supplies have been agreed with Central Asian states to the north, but given its access to major ports on the Caspian Sea and the Gulf, Iran would be an invaluable transit route, though the likelihood of military supplies coming through Iran is a distant prospect.
Trade between Iran and Afghanistan is already strong, facilitated by a well-paved highway built by Iran, which crosses the border into the western Afghan province of Herat.
"If the relationship between the U.S. and Tehran stabilises, things will be much better for us in Afghanistan," said Davood Moradian, senior policy advisor at the Afghan foreign ministry.
Iran shares a common language and cultural and historical ties with Afghanistan, but it has been an avowed enemy of the United States since the 1979 Islamic Revolution and its relationship with Afghanistan has been complex.
"As a whole Iran's contribution has been constructive and positive, but there are some in Tehran who are still ambiguous about Afghanistan ... because the U.S. is here and because we are an emerging democracy," Moradian said.
While Iran and the United States sat at the same table to discuss Afghanistan's future after the Sept. 11 attacks, the Bush administration, wary of Tehran's nuclear ambitions, made sure the new pro-Western Afghan government kept Iran at arm's length.
The Bush administration repeatedly stated that all options were open if Tehran developed nuclear weapons, a thinly veiled threat of attack, heightening the insecurity already felt by Iran with already 30,000 U.S. troops in Afghanistan to its east, and another 140,000 in Iraq to its west.
Iran's defence has been to make sure those troops are either too tied down fighting insurgents to pose a threat, until, as in the case of Iraq, its influence and interests are assured.
Though Shi'ite Iran is no friend of the Taliban and almost launched its own war to overthrow the austere Sunni Islamist movement in 1998, Tehran is not above drip-feeding supplies to Taliban militants, military sources say: not enough to hand them victory, but enough to sap U.S. military strength.
"The Iranians have an influence inside Afghanistan ... and Iranian-origin improvised explosive devices (IEDs) appear inside Afghanistan," said a NATO diplomat, who requested anonymity.
"There may be elements inside the Iranian government or military of one kind or another that may be providing these."
Taliban expert Rashid said the Iranians have stepped up their support to dissident groups inside Afghanistan, "not necessarily as political proxies -- because clearly they don't want the Taliban back -- but as forces who could disrupt the U.S. if there was going to be an attack on Iran".
Using military proxies is a tactic of both the United States and Iran, and if the two sides were to narrow their differences -- removing the need to support groups with which they would otherwise be at odds -- Afghanistan could be more stable.
"A lot of the countries in the region that have involuntarily become the battleground for U.S.-Iranian rivalry can only benefit tremendously if that rivalry will transform into a more collaborative relationship," said Trita Parsi, president of the Washington-based National Iranian-American Council.
But Iran also has good reason for wanting a more stable Afghanistan, both to boost trade and to stem the flow of Afghan drugs that feed the habits of some 1 million Iranian addicts.
That is something the Obama administration can appeal to, but more than anything else Washington will have to convince Tehran that its presence in Afghanistan does not pose a threat to Iran.
"The critical thing ... is that the Americans give assurances to Iran that they will not use Afghan soil to destabilise Iran," Rashid said.
Additional reporting by Sue Plemming in Washington and David Brunnstrom in Brussels