MOSCOW, Sept 11 (Reuters) - Russia sent Tajikistan 12 armoured vehicles and an array of military equipment, its defence ministry said on Saturday, as Moscow looks to shore up its Central Asian ally that neighbours Afghanistan. Moscow has held military exercises in Tajikistan and expanded hardware at its military base there, its biggest in a foreign country, since the U.S. withdrawal of troops from Afghanistan and the Taliban"s lightning takeover. Russia is worried about the potential for fallout in the wider region and the possibility of Islamist militants infiltrating Central Asia, which Moscow sees as its southern defensive buffer. "Against the backdrop of growing instability near Tajikistan"s southern border, we are working together to ensure the security of our states," said Major General Yevgeny Tsindyaikin in a defence ministry statement. The transfer of hardware, which also includes close combat equipment and protective gear, will modernise and significantly enhance Tajikistan"s military capabilities, the ministry said. Tajikistan"s border with Afghanistan stretches for 1,344 km (835 miles), and much of it is mountainous and hard to police.