A military police helicopter crashed in south-western France on Friday, killing four gendarmes on board, local authorities and the national military police said.The accident occurred during an exercise, the National Gendarmerie, a military police unit, said. Interior Minister Bernard Cazeneuve said in a statement that the training had taken place at Vignemale, one of the highest peaks in the French Pyrenees along the border with Spain.During the training, the helicopter that they were on board crashed, Cazeneuve said. He added that the circumstances of the crash remain unclear.Two of the gendarmes were part of the aerial division, and two were part of the mountain division.A crisis cell was set up following the crash, local authorities for the mountainous Hautes-Pyrenees region said on their Twitter account. Cazeneuve said he would travel to the area Friday evening."I express my emotion after this tragic accident. I address my condolences to the families and those close to the victims, and testify to the solidarity of the nation in these painful circumstances," President Francois Hollande said in a statement.