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Dressed smartly in their new yellow and green uniforms, students at the Tajik Border Guard Academy salute their commander, Gen Nasrullo Gurayev.

Battle-hardened during Tajikistan's civil war in the 1990s, Gen Gurayev has headed the academy for several years.

His time as commanding officer will be remembered partly because the academy has recently had a major facelift.

US government money has helped turn a crumbling Soviet-era compound into a modern training facility for Tajikistan's future border guards.

Their training is important. Tajikistan shares almost 1,400km (870 miles) of mountainous border with Afghanistan, a frontier that is challenging to police.

Until 2005, Tajikistan's former master, Russia, helped patrol it.

But after the Russians left, the US began assisting with border security. Last year, Washington invested $15m (£9.4m) in various projects from border guard training to supplying outposts with modern equipment.

"Drugs, arms and terrorists can flow across the border," said the US ambassador to Tajikistan, Ken Gross.

"We try to maintain a fairly high level of assistance to make sure that they are able to control the border."

Part of the reason the US is spending money in Tajikistan is because the Central Asian nation is on a new supply route for US and Nato troops fighting in Afghanistan.

The route is known as the Northern Distribution Network, the NDN.

It is a series of rail, water and road links via Russia, the Caucasus and Central Asia through which non-lethal military cargo such as construction materials, fuel and medicine is transported to troops in Afghanistan.

The NDN is an alternative to the main supply route via Pakistan which is under constant Taliban attack. According to the US Transportation Command, 40% of supplies for US and Nato troops are now shipped via the NDN.

"NDN is designed to make sure that we are able to fully support our troops, fully support our development efforts in Afghanistan, so that we don't have just one route that we have to rely on," said Mr Gross.

The US has a long-term aim of boosting trade between Afghanistan and its Central Asian neighbours. For this purpose in 2007 it built a major bridge linking Afghanistan with Tajikistan.

Although most of the NDN cargo enters Afghanistan via Uzbekistan, the Nizhny Pyanj bridge also serves as an important connection point.

Trucks that carry US and Nato supplies are unmarked for obvious reasons. They may come under attack within Afghan territory, but while no attacks on NDN shipments have so far been recorded, there is concern that this may change in the future.

Tajikistan already has major security challenges, with reports of armed drug gangs making incursions into Tajik territory.

In September the government claimed to have killed 20 Taliban fighters trying to cross the border. An upsurge in violence in northern Afghanistan is also a concern.

"There are many Taliban fighters who have been pushed into northern Afghanistan, that's why there is a real threat," said Khushnud Rahmatulayev, a spokesman for the Tajik Border Services.

"But Tajikistan is ready to repulse them."

In addition to reported incursions, however, there has also been a decline in the internal security situation.

More than 60 soldiers and special forces personnel have been killed in incidents this autumn.

A troop carrier was ambushed by armed fighters in the country's east and a helicopter came down in suspicious circumstances.

Tajikistan was also shaken by its first suicide bombing in September against a police station in the northern town of Khujand. Two officers were killed.

The government blames religious extremists for the violence and recently launched a campaign to bring back young Tajik men studying at religious schools abroad.

President Emomali Rahmon has publicly claimed that many scholars are returning home as terrorists.

"The recent events here indicate an internal crisis of power. All of the state structures are weak. Everything that has been done up to now, what they call state-building, has failed, " says Dushanbe-based political analyst Saimutdin Dustov

US and Nato leaders do not want Tajikistan to import Afghanistan's problems.

But the security of this little country also depends on internal stability. Failure in Tajikistan will have consequences for the wider Central Asia region.