Iran's broadening influence beyond its border with Iraq, together with its pursuit of nuclear technology, has Europe and the US on alert.
Now, its role along its opposite border here in Afghanistan is facing scrutiny, as well. It was a source of disagreement between President Bush and Afghan President Hamid Karzai during the past two days of talks at Camp David.
Mr. Karzai told CNN just before his meeting with Bush that Iran "has been a helper and a solution."
But key members of the Bush administration disagree, with Mr. Bush saying Aug. 6 that the burden was on Iran to prove that it is not a "destabilizing force."
Both views could be correct, say experts and Afghan officials, and they reflect the subtlety of Iran's efforts to play both sides – to support the fledgling Karzai government, yet also to secure its own strategic aims in the region and beyond.
The interception of Iranian-made weapons in Afghanistan, as well as reports of increased insurgent activity along the Iranian border, are seen as a message to the West, in particular.
"They're saying, 'We're cooperating on the ground,' " says Amin Tarzi, director of Middle East Studies at Marine Corps University in Quantico, Va. " 'But we can make a mess for you much bigger than Iraq' " if Europe and the US keep threatening action against Iran's nuclear program.
Iran plays two games in Afghanistan
Since the fall of the Taliban in 2001, Iran has been a useful neighbor to Afghanistan, maintaining peace along its border and undertaking a variety of development projects, particularly here in the border province of Herat.
Given that Iran and the Taliban were enemies who nearly went to war in 1998, "Iran benefited from the fall of the Taliban, too," says Sultan Ahmad Baheen, spokesman for the Afghan Ministry of Foreign Affairs.
Yet even as Afghanistan maintains a diplomatic gloss toward its powerful neighbor, Afghan government officials are worried that Iran is meddling to gain leverage on a variety of issues, both within the country and with the Western nations whose troops are deployed here.
"Iran is playing two games," says Mohammed Rafiq Shahir, president of the Council of Professionals, a group of analysts and businesspeople in Herat.
"The first policy is to support the government because it prefers this to the Sunni extremists of the Taliban," he says. "The second game is an anti-American policy: Whatever they can do to defeat Americans here, they will do it."
Iranian officials have repeatedly denied such allegations. Indeed, it is a matter of tradition in Afghanistan to blame the nation's woes on the interference of outsiders. But normally, such allegations are levied primarily at Pakistan, whose intelligence services are seen as funding and harboring Taliban leadership. By contrast, Afghanistan's relations with Iran during the past six years have been cordial, even exceptional.
"For most of the past few years, Iran has always been singled out as an exemplary neighbor by all sides," says Professor Tarzi.
It is one reason that Karzai would be loath to enter a war of words with Iran, experts say. He cannot afford to alienate what has been a close and peaceful ally. But some government officials are voicing concerns about what they call Iran's cautious yet deliberate efforts to gain influence in Afghanistan recently.
After years of goodwill, the criticism suggests a gradual shift in the relations of the two countries. There is no irrefutable evidence of wrongdoing, officials say, but rather a mounting of clues.
In recent weeks, the commander of the Afghan Border Police for the region bordering Iran, Col. Rahmatullah Safi, has been outspoken about Iran. In addition to the seizure of Iranian-made weapons in his territory, he alleges that Iran is harboring a hit squad led by former mujahideen commander Yahya Khortarak, which targets local leaders. Other security officials suggest that there is an Iranian terrorist training camp near the Afghan border.
It is doubtful that Iran would want to topple the Karzai regime, analysts say. Under the inclusive Western-backed government, Shiites have unprecedented power, despite the fact that they make up only 12 percent of the population. As a center of Shiite power, Iran would not wish to threaten such a delicate sectarian balance.
But with Europe and the United States talking tough about Iran's nuclear program, Afghanistan represents an opportunity for Iran to shift circumstances in its favor. "They're always trying to gain more leverage in these talks," says Tarzi.
Afghanistan struggles with refugees
The same is true with regard to Afghanistan itself. Earlier this year, Iran began deporting thousands of Afghan refugees. Though Iran was perfectly at liberty to do so, the abruptness of the decision, combined with the sheer number of deportees and the fact that many of them had legal documents to remain in Iran, pointed to a motive beyond expedience or impatience.
Water-rights issues of crucial importance to Iran are now in the balance, as well as Afghanistan's willingness to support the US and Europe in their anti-Iran campaign. The sudden arrival of thousands of jobless Afghans into a country ill-prepared to absorb them was designed to remind Kabul of Iran's ability to make life difficult for Afghanistan, critics say.
Here, along Afghanistan's border with Iran, beneath a massive admonitory portrait of Ayatollah Khomeini, the buses still often come more than once an hour.
They bring Afghans like Mir Mohammed Safari, a teenager who says he lived in Iran legally for seven years before being rounded up from his workplace without notice, taken here, and then shunted unceremoniously across the border.
He is one of thousands of Afghan workers who fled to Iran, either for safety or employment, who are now being thrown out.
For his new life in Afghanistan, he has only what he could fit into a plastic bag. "From everything, I brought this," he says with a wry smile.
Fellow refugee Javed Sharifi squints in the sunlight, as the wind whips violently over this arid border checkpoint.
Mr. Sharifi has only 500 Afghanis – $10 – to try to get to his home on the opposite side of Afghanistan, some 400 miles away. Says Sharifi: "I have no idea how I am going to get to Takhar."
• Mr. Sappenfield is the New Delhi correspondent for the Monitor and USA Today.