Last week, high-profile delegations from the region’s main security arbiters, the United States and Russia, converged on Tajikistan’s capital, Dushanbe, for separate talks with the government on protecting the border. With violence in northern Afghan provinces on the rise, there are budding fears about what the absence of American troops might mean.

“Tajikistan and also Uzbekistan and Turkmenistan, all the republics on the northern border with Afghanistan, are facing serious threats to their security,” said Suhrob Sharipov, director of the Center for Strategic Studies, a government-connected policy group in Dushanbe. He said the United States must make every effort “to conduct the withdrawal of forces from Afghanistan painlessly.”

An extremely poor, mostly Muslim nation of about 7.6 million people, Tajikistan shares an 870-mile border with Afghanistan, the longest after the one with Pakistan. It is a porous and in some places intangible boundary that hews closely to the River Panj, with a smattering of poorly trained, undereducated and easily corruptible guards deployed to protect it.

Possible militant incursions into Tajikistan have put the government here increasingly on edge. The authorities blamed Islamist fighters with links to Afghanistan and Pakistan for an attack on a military convoy that was reported to have killed two dozen troops in September. In the past year, Tajik forces have raided the craggy mountain hideouts of suspected militant leaders, arresting or killing several.

Yet the extent of the militant threat is unclear. The authoritarian governments of Central Asia have long used the specter of Islamic radicalism to justify crackdowns on dissent. Tajikistan’s president, Emomali Rakhmon, a former Communist Party functionary, has imposed ever-increasing restrictions on observant Muslims, most recently pushing through a law that will bar children under the age of 18 from attending mosques.