 Complete the following phrase:  In mid-March, unidentified airplanes dropped bombs onto villages in the vicinity of Srebrenica violating the No-Flight zones for the first time. The Bosnian Serbs were accused of responsibility for the bombing but denied it. On 31 March, a resolution was voted authorising the nations contributing to UNPROFOR to take all necessary measures to prevent military flights from the belligerents in the no-flight zones 