Afghan politicians, media, and even some repatriated refugees say they think the mass evictions since mid-April are an attempt by Tehran to destabilize western Afghanistan.
With tension heightened between Washington and Tehran over Iran's controversial nuclear program, analysts say such fears are understandable.
The discovery of Iranian-made weapons that NATO says were bound for Taliban fighters has fueled further concern.
But while experts on South Asia interviewed by RFE/RL said they thought Tehran would like to prevent the U.S. military from building up a strategic airfield near Afghanistan's western border with Iran, they expressed doubt the Iranian government was using mass repatriations and weapons smuggling to try to achieve that goal.
Since 2003, the U.S. military has been developing the strategic Shindand airfield near Iran, in the western Afghan province of Herat.
Ian Kemp, an independent defense analyst in London, said the presence of U.S. forces at Shindand is seen by Tehran as a threat because Shindand could serve as a launching point if the United States decided to attack Iran's nuclear facilities from the air.
"The Iranians have a significant military capability," Kemp said. "They are likely to offer far greater resistance [on the ground] than the Iraqi forces did. And with the U.S. and its allies being bogged down in Iraq and Afghanistan at the moment, any form of conventional military action on the ground [against Iran] can be ruled out of the question. I think if the United States was to decide upon military action, a combination of missile strikes using sea and air-launched cruise missiles and air strikes would probably be the preferred option."
Making Things Difficult
Peter Lehr, an expert on South Asia at St. Andrews University in Scotland, said the Iranian government might be trying to complicate the situation for U.S. forces in western Afghanistan by sending thousands of Afghan refugees there.
"That's a kind of war by proxy," Lehr said. "If you take a look at other borders between Pakistan and India -- especially the Kashmir problem -- you see that Pakistan is busily exporting many of these former Afghani fighters into Kashmir so that it can raise some troubles there and keep the Indians busy. With the same logic, you can say that Iran is trying to get as much mileage out of the refugee crisis as they can get just to annoy the Americans. That's the way to fight back against the Americans. [Iran] can't come out with [naval war ships]. They can't come out with sophisticated [war planes]. What they can do is things like hostage taking, sending out some agents. What they can do is send a deluge of refugees across the border. That's possible."
Pakistani journalist and author Ahmed Rashid said he thinks the repatriation of thousands of Afghan refugees by Tehran could destabilize the Afghan government and cause problems for U.S. forces at Shindand.
"That's a possibility," Rashid said, "but I don't think [Iranian officials] need to do that, because they have long-running relations with many of the commanders and small-time warlords in western Afghanistan -- both Pashtun and non-Pashtun."
Still, regardless of whether Afghan refugees are being used as pawns in a geopolitical struggle, Rashid said he is convinced that Tehran wants to make life more difficult for U.S. forces in Afghanistan.
"I have no doubt that Iran has been involved in channeling money and arms to various elements in Afghanistan, including the Taliban, for the last few years," Rashid said. "I think Iran is playing all sides in the Afghan conflict. There are Pashtuns and non-Pahstuns who are being funded by Iran who are active in western Afghanistan. If the Iranians are convinced that the Americans are undermining them through western Afghanistan, then it is very likely that these agents of theirs have been activated."
'Confrontation By Proxy'
British Defense Secretary Des Browne has suggested that Iran might be helping Taliban forces that are fighting NATO troops in Afghanistan.
Browne told the House of Commons Defense Committee in London on May 8 that Iran has "sought confrontation by proxy" with Britain and the United States, as well as other NATO members, in the Middle East. Without elaborating, Browne said there is "some indication" that Iran is doing the same in Afghanistan.
But Lehr said he is suspicious of claims that Iranian agents slipped into Afghanistan alongside the thousands of repatriated refugees in order to instigate recent violence near the Shindand airfield.
Lehr said he also doubts suggestions by U.S. and British officials that the Iranian government has been directly involved in supplying weapons to the Taliban.
"I see a connection to this nuclear issue," Lehr said. "The United States are desperately looking for a casus belli, in my opinion. Of course, it is tempting for [Iran] to instigate even more hatred against the Americans around this very air base. They are deniable effects; if some of these people get caught, well, they can always deny that they are working for the Iranian government. But if you take a look at the context -- at this nuclear issue -- and if you take a look at the fact that the Americans tried to link up a weapons shipment from Iranian territory into Afghanistan with the politics of the Iranian government, then it starts to get a bit smelly."
One of Lehr's areas of expertise is the organized criminal groups that smuggle illegal drugs from Afghanistan to Western markets. He says drug payments made by those groups are much more likely to be the reason that Iranian weapons are being found by NATO soldiers in western Afghanistan.
"If you take a look at the weapons smuggling, well that's been going on for decades," Lehr said. "That is part of this drug route where heroin is shipped from Afghanistan via Iran and other countries and Russia to Europe. The best way of paying for drugs is either, of course, with money -- or with weapons. And there is not even circumstantial evidence that the Iranian state, itself, is involved with that. That is organized-crime groups."
Afghan media and politicians speculate that one reason for Iran's expulsion of refugees probably is to show that it can indirectly pressure the United States by contributing to an economic crisis in Afghanistan.
They said another reason could be the internal economic difficulties now facing Iranian President Mahmud Ahmadinejad's administration. Sanctions against Iran have contributed to inflation and unemployment there. The expulsion of 1 million Afghan refugees could be seen by Tehran as a way to increase employment opportunities for Iranian citizens.