More than 10,000 troops, mostly Tajik reservists, will take part in the first such drills in the area by the ex-Soviet allies, Tajikistan's defence ministry said.

Combined forces will practice "eliminating terrorists who broke through" from Afghanistan in an imagined incursion, it said.

Some 400 soldiers and 80 pieces of Russian military equipment were deployed from a military base in Tajikistan for exercises due to last until Friday, the Russian army said.

The drills will take place just over the border from the Afghan province of Badakhshan.

Russia and Tajikistan have intensified military cooperation since US-led forces began withdrawing from Afghanistan in large numbers in 2014.

This is the first time they have held exercises in the sometimes restive Tajik province of Gorno-Badakhshan, where clashes between government and rebel forces took place in 2012.

Previous exercises were held in the country's southern Khatlon province.

China has beefed up its security assistance in the country in recent times, notably building infrastructure on the 1,300-kilometre (800-mile) border between Tajikistan and Afghanistan and holding its own drills with Tajikistan in 2016.

The border is a haven for drug traffickers and was guarded by Russian troops before they stepped back in 2005. Afghanistan is the world's biggest opium producer.