BUCHAREST (Reuters) - Romania has expelled a pro-Russian Serbian nationalist and banned him from entering the NATO member for 15 years after he showed an interest in obtaining classified information on  military installations, state security said on Tuesday. Bratislav Zivkovic, 42, is a commander of Serbia s Chetnik paramilitary and went to Crimea in 2014-15 to support the Russian intervention there. He told reporters there at the time that it was only natural to want to help Russians fighting the Ukrainians.  A spokesman for Romania s SRI secret service said it had identified Zivkovic  showing interest in obtaining classified documents on critical infrastructure and national and allied military objectives located in south-east Romania with the intention of affecting our strategic partnerships.  SRI s Ovidiu Marincea said Zivkovic had been caught while taking photos of military radars on the Black sea shore and  trying to transmit their GPS coordinates.   I want to stress this Serbian citizen did not succeed in gathering any documents or classified information,  Marincea said. He poses a risk to Romania s national security, he added. Russia is Serbia s traditional ally with the two nations sharing Slav origins, the Christian Orthodox faith and having similar languages. Serbia is heavily dependent on Russia s energy and the cash-strapped government in Belgrade has turned to Kremlin to underpin its budget. The Serbian Chetniks gained notoriety in the 1990s when their units committed atrocities against non-Serbs in Croatia, Bosnia and Kosovo, a former Serbian province dominated by ethnic Albanians. 