Iran continues to amass its military forces along this tense border with Afghanistan. Whether its troops cross over may ultimately depend on who wins a power struggle back in the capital, Tehran.
Iranian options range from armed attack to diplomatic persuasion, but few offer the solace or revenge that many Iranians expect, diplomats and analysts say. And Iran's internal battles between reformist and conservative clerics may dictate events.
The Islamic republic is at odds with Afghanistan's ruling Taliban, whose extreme brand of Sunni Islam is viewed as a threat by largely Shiite Iran, which seeks to retain a strategic role in Afghanistan and protect ethnic minorities it backs.
The Taliban has taken control of most of the country, pushing out minority opposition militias. In recent weeks Taliban forces overran two opposition strongholds, leaving thousands dead in Mazer-i-Sharif, including eight Iranian diplomats and a journalist. The Taliban still holds dozens of captured Iranian citizens.
The Iranian buildup along the border underscores how seriously the threat of force is being considered. Officially, some 270,000 troops - half the estimated armed forces of Iran - are conducting exercises. Western sources suggest the actual total may be a fraction of that number.
But in Mashhad, in one of several military parades to mark "Sacred Defense Week" across Iran Sept. 25, thousands of soldiers and Revolutionary Guards marched in long columns, some with turbans or gas masks and assault rifles. Women, too, draped in black chadors with red revolutionary headbands, formed an armed river of black.
"Diplomacy is now being pursued, but it appears that we must also show our teeth to the Taliban," says Sadiq Zibakalam, a political scientist at Tehran University whose critical writing about Iran's "blunder" in Afghanistan has raised the ire of the Foreign Ministry.
"Afghanistan is like a swamp, and once we get in we will never get out," he says. "Either we must destroy the Taliban, which we cannot do, or we must tame the Taliban" by creating a dialogue that will influence them.
Iran's military establishment disagrees, at least in public, and says that only the threat of force will keep the Taliban, which is mostly ethnic Pashtun, from harming the Hazara, Tajik, Uzbek, and other minorities.
"Some people say that Afghanistan is a quagmire, but that is not true," says Minister of Defense Ali Shamkhani. "Today international opinion is for us and against the Taliban, and if this continues they will support anything we do."
But any Iranian decision to act may not be based on hard-nosed strategic calculations. Reformist President Mohamad Khatami is under fire from conservative clerics who challenge his moves to open Iran to the rest of the world, and to loosen tough social restrictions that have dominated since the 1979 Islamic revolution.
"If Iran can get a strong enough condemnation of the Taliban from abroad to justify not attacking, that would suit the reformers," says a Western diplomat. The United Nations last week agreed to seek a non-military solution and dispatch a UN envoy.
"But the hard-liners may see a little war to their advantage, to turn the focus away from domestic criticism," he says. "Another problem is that Iran has a lot of 'face' involved in the military buildup, and can't wind down without doing something."
One option is to arm some of the 1.4 million Afghan refugees now in Iran and send them back across the border as recruits.
Deposed Afghan President Burhanuddin Rabbani - who was forced from Kabul in 1996, but whose "government" still holds the Afghanistan seat at the UN - has openly called for arming the refugees, and his request was echoed by some clerics in Iran.
Pakistan backs the Taliban with materiel, cash, and "volunteers" - with funding from Saudi Arabian sources. Those two countries, along with the United Arab Emirates, are the only three that recognize the Taliban government. Iran has backed the opponents, but infighting has led to the recent defeats.
For Afghans in Mashhad, however, there is a brave face of optimism. "The Taliban alone is nothing, it can be removed in a day. But their band of foreign supporters is what keeps [it] going," says Tourayalai Ghiyasi, the Iran representative of Ahmed Shah Masoud, the Afghan warlord fighting the Taliban in the northeast.
The Taliban has brought a sense of security to areas under its control, where militias once battled over fiefdoms. But in accordance with the Taliban's interpretation of Islam, which has drawn fire from international human rights groups, women must follow extreme restrictions. Men whose beards are not sufficiently long have been beaten.
"There is a new culture ruling us, and the Taliban have a very bad attitude," says an Afghan refugee teacher. "It means there is no life in Afghanistan, in reality. There is peace, but no life."