BLIDA, Algeria — A military transport plane slammed into a field near the Algerian capital Wednesday, killing at least 257 people in the North African nation’s worst aviation disaster.

It was not immediately clear what caused the crash, which occurred shortly after takeoff from the Boufarik military airport, 16 miles southwest of Algiers. The army’s chief of staff, Maj. Gen. Ahmed Gaid Salah, went to inspect the site and ordered an investigation, the Ministry of National Defense said in a statement.

The victims consisted of 247 passengers — most of them soldiers and their families — and 10 crew members, the statement said. There was no mention of any survivors.

The Polisario Front, an Algerian-backed movement that seeks independence from Morocco for the Western Sahara region, said 30 of its people were among those killed. They were refugees, including women and children.