MOSCOW, July 8 (Reuters) - The U.S. exit from Afghanistan is a headache for Moscow which fears spiralling fighting may push refugees into its Central Asian backyard, create a jihadist threat and even stir civil war in one ex-Soviet state, a former Russian diplomat and two analysts said. U.S. forces vacated their main Bagram Air Base last week and most NATO forces have also pulled out. That has emboldened the Taliban, which has made territorial advances, raising fears about the Kabul government"s grip on power and prompting over 1,000 Afghan security personnel to flee to Tajikistan. The turmoil is a worry for Russia because it regards the region, part of the former Soviet Union once ruled from Moscow, as its southern defensive flank and as a sphere of influence from which radical Islamist threats could emanate. Moscow, still haunted by its own 1979-89 Afghan war, is unlikely to engage militarily in Afghanistan, Sergei Lavrov, Russia"s top diplomat, has made clear. read more But a refugee exodus into Tajikistan, an impoverished nation of 9.3 million which fought a civil war involving Islamist forces from 1992 to 1997, would pose a humanitarian challenge and could be infiltrated by Jihadists, the three sources said. Uzbekistan or Turkmenistan could also face blowback. "The most vulnerable seems to be Tajikistan where the state is brittle and in the midst of the hereditary succession to (President Emomali) Rakhmon"s son," said Vladimir Frolov, a former senior Russian diplomat. "The risk is in jihadi forces exploiting the existing social divisions and the clamour for justice to reignite the civil war," he said. Russia"s largest foreign military base is located in Tajikistan near the Afghan frontier and comprises around 6,000 soldiers, tanks, armoured personnel carriers, drones and helicopters. It also has an airbase in neighbouring Kyrgyzstan. President Vladimir Putin told Rakhmon on Monday that Moscow would help Tajikistan handle any fallout if needed. Rakhmon has ordered the mobilisation of 20,000 military reservists to bolster the border and asked a Russian-led regional military bloc for help. read more "Another threat is in Turkmenistan which is not really a state and does not fully control its borders with Afghanistan. There, all bets are off," Frolov said. Afghanistan remains seared on Russia"s national conscience over thirty years after the Soviet Union ended its own military campaign after losing the lives of 14,000 nationals. "I don"t think they"re considering a direct military engagement in Afghanistan. It"s too sensitive an issue for many Russians," said Andrey Kortunov, head of the Russian International Affairs Council, a think tank close to Russia"s Foreign Ministry. For Moscow, he said border security was key along with sharing data on anti-terrorist activities, counter-intelligence and special operations. ZERO-SUM GAME Moscow"s goals are to prevent Afghanistan becoming a platform for international terrorism and to erode its role as a major heroin exporter, said Kortunov. Working with the Taliban, which Russia formally considers a terrorist group but has hosted in Moscow for peace talks, is part of its plan, all three sources said. A Taliban delegation visiting Moscow on Thursday said the Taliban would not attack the border with Tajikistan or allow Afghanistan to be used for attacks on Russia, the TASS news agency reported. read more Arkady Dubnov, a Moscow-based analyst, said Russia had been careful not to criticise the Taliban in recent statements. "Moscow is betting the Taliban is a largely local tribal force that does not have interest or aspirations to project its power and control beyond the borders of Afghanistan," Frolov said. "The bet is that not waging war on the Taliban (even in propaganda terms) will pay off by finding a ... modus vivendi with the new government in Kabul controlled by the Taliban," he said. The scenario Moscow wants to avoid is NATO redeploying from Afghanistan to Central Asia. "This (exit) process...cannot and must not turn into a redeployment of U.S. and NATO military infrastructure facilities to countries neighbouring Afghanistan, especially in Central Asia," Zamir Kabulov, Russia"s special representative on Afghanistan, said last week. While Lavrov on Wednesday said the U.S. exit was "hasty", hawkish factions in Russia have long wanted the West out of Afghanistan. Dubnov said that aspiration risked backfiring. "Moscow and Washington have always played a zero-sum game in Afghanistan - what was bad for the States was good for Russia and vice versa," he said. "Now there"s a new phase in the war and what is good for America, which is finally withdrawing its forces, turns out to be bad for Russia."