MOSCOW, July 6 (Reuters) - Russian military helicopters based in Tajikistan fired air-to-surface missiles during a training exercise on Tuesday as Moscow said its forces in the Central Asian nation were fully equipped to help secure the border with Afghanistan. Tajik President Emomali Rakhmon on Monday ordered the mobilisation of 20,000 military reservists to bolster the border with Afghanistan after more than 1,000 Afghan security personnel fled across the frontier in response to Taliban militant advances. Russian President Vladimir Putin told Rakhmon on Monday that Moscow would help the impoverished former Soviet republic contend with the fallout from NATO"s exit from neighbouring Afghanistan if necessary. Russia, which operates one of its largest military bases abroad in Tajikistan equipped with tanks, helicopters, drones and ground attack aircraft, would help stabilise the border with Afghanistan if needed, both directly and through a regional security bloc, the Kremlin said in a statement. Government forces plan a counteroffensive in Afghanistan"s northern provinces after losing ground to the Taliban, Russia"s RIA news agency quoted an adviser to Afghan President Ashraf Ghani as saying on Monday. Government forces plan a counteroffensive in Afghanistan"s northern provinces after losing ground to the Taliban, Russia"s RIA news agency quoted an adviser to Afghan President Ashraf Ghani as saying on Monday. Russia"s Deputy Foreign Minister Andrei Rudenko repeated that pledge on Monday and was cited by the Interfax news agency as saying it appeared that the Taliban was now in control of most of the border on the Afghan side. "The situation there is rather tense because according to some sources, up to 70% of the Tajik-Afghan border is now controlled by the Taliban," Rudenko was quoted as saying. Russia"s defence ministry said on Monday that two MI-24 attack helicopters and two military transport helicopters had taken part in a training exercise in Tajikistan during which unguided missiles had been launched at more than 15 ground targets. The exercise had simulated an attack on illegal armed groups along with a convoy of cars, enemy firepoints and arms caches.