A Ukrainian drone on Saturday breached Bulgaria's airspace and directly endangered vital energy infrastructure upon exploding in Bulgarian territory, regional media reports. File image via ReutersBulgaria's defense ministry quickly pointed the finger at Kiev, saying the destroyed drone debris points to a weapon "widely used by the Ukrainian military." Despite the two countries by and large being 'friendly' - Bulgaria has summoned the Ukrainian ambassador for a meeting scheduled for Monday in response, AFP reports. According to Bulgarian Prime Minister Rumen Radev, the drone entered Bulgarian airspace from Romania before exploding 1,000 metres from a compressor station of the Trans-Balkan gas pipeline, near the former Kardam border checkpoint between the two countries. Bulgarian Prime Minister Rumen Radev has expressed the main concern, saying the explosive payload the UAV carried was "significant".