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 ("Operation Deny Flight"). French, Dutch and American airplanes were deployed to enforce the resolution. In total, until 1 December 1994, 3317 violations were observed. On 28 February 1994, four military aircraft were shot down by NATO fighters over Bosnia and Herzegovina.