A bus carrying university students on a pre-graduation trip toppled off a mountain cliff in southern Albania on Monday, killing 12 people and injuring another 21, AP quoted authorities as saying. University officials said two buses had been taking 75 third-year language and literature students and three professors from Aleksander Xhuvani University in the city of Elbasan on a trip to the southern city of Saranda. One bus carrying 33 people fell 80 meters (yards) off the road near the town of Himare, 137 miles (220 kilometers) south of the capital, Tirana, police spokeswoman Klejda Plangarica said. The cause of the crash was unclear. Albanian media quoted one of the passengers and a resident near the crash site as saying the bus had been going very fast. Albania's transport minister also said the road had been recently repaired. Fourteen of the injured students were in serious condition and were flown by helicopter to Tirana's military hospital. One died on the way, raising the total death toll to 12. Local prefect Edmond Velcani said the bus driver was among the dead. Prime Minister Sali Berisha sent condolences to the families of the dead, speaking from Chicago, where he was attending a NATO summit. President Bamir Topi and main opposition Socialist party leader Edi Rama visited the hospital and Rama donated blood for the injured. The government declared a national day of mourning Tuesday, with flags at half-mast and public television broadcasting classical music. It will also pay all funeral expenses.