Ten victims from a bus crash that killed 14 people in North Macedonia have been buried in the western city of Gostivar, as authorities are still trying to determine the causes of the accident.

Prosecutors say tests showed the driver of the bus that drove off a highway embankment and overturned Wednesday had not been under the influence of alcohol or drugs.

Authorities have requested assistance from telecommunications operators to see whether the driver — who survived the crash — had been on his cellphone at the time of the accident west of the capital, Skopje.

Health officials said Friday that six people were still hospitalized in life-threatening condition. The bus had been carrying 51 passengers, mostly students and office workers, from Skopje to Gostivar.

Police officers stand near the bus wreckage at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police officers stand near the bus wreckage at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police and investigators stand near the bus wreckage at the crash site at the village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police and investigators stand near the bus wreckage at the crash site at the village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
A bus lays overturned at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
A bus lays overturned at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police officers and investigators are silhouetted at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police officers and investigators are silhouetted at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
A bus lays overturned at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
A bus lays overturned at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police and investigators stand near the bus wreckage at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)
Police and investigators stand near the bus wreckage at the crash site at village of Laskarci, west of Skopje, North Macedonia, Wednesday, Feb. (AP Photo/Boris Grdanoski)