KIEV (Reuters) - The destruction of two ammunition depots this year have dealt the biggest blow to Ukraine s combat capability since the start of its separatist conflict, security and military officials said on Thursday. Massive explosions at a military depot in the Vynnytsya region, 270 km (170 miles) west of Kiev, forced the authorities to evacuate 24,000 people on Wednesday. Another large depot was destroyed in March. It is not clear if the explosions were accidents or sabotage, either of which would underscore poor security at the bases, but officials traded blame for the resulting losses.   The country has suffered the biggest blow to our fighting capacity since the start of the war,  the secretary of the Ukrainian Security and Defence Council, Oleksandr Turchynov, told journalists. Earlier the defense ministry said the Vynnytsya depot contained 83,000 tonnes of ammunition.  There are many violations of fire and air safety at our arsenals. And these are the consequences,  Turchynov said.  We ve shown that we re not capable of protecting our strategic arsenals.  Prosecutors have launched an investigation into the Vynnytsya blaze, which the authorities have said may have been started deliberately, citing  external factors . Chief military prosecutor Anatoly Matios said the site s alarm system was out of order and its security team lacked sufficient guards and up-to-date equipment.  The main issue which must be addressed is the personnel problem of guards whose salaries are very low, and in general security is carried out by elderly people, who certainly don t have hawk-eye vision,  Matios told journalists. There have been four large fires at ammunition and weapons depots since late 2015 - an additional drain on Ukraine s military, which has been fighting Russian-backed separatists in eastern regions for more than three years.  It will be hard for the government to restore the military reserves that have destroyed by explosions over the past two years. This is hundreds of billions of hryvnias,  Matios said. Both Matios and Turchynov said Ukraine s General Staff, which is responsible for the military s day-to-day operations, should be held accountable for security failings at the depots. In a post on Facebook, Chief of the General Staff Viktor Muzhenko denied accusations his institution was incompetent. The comments were intended to  sow doubt about the armed forces  ability to protect its people, (and) undermine trust in the army,  he said. 