Funerals were held Friday for the victims of a train crash in the capital Ankara on Thursday, while workers were still clearing the debris left in the wake of the collision with a railway engine.

The cause of the crash that killed nine people is still unclear, while teams led by three prosecutors investigated why the high-speed train heading to the central city of Konya from the capital hit an engine tasked with checking the tracks head-on.

Ebru Erdem Ersan, Tahsin Ertaş and Berahitdin Albayrak were buried after funerals in Ankara.

Ersan, a 38-year-old mother of two, was a businesswoman traveling to Konya for work, while Ertaş was commuting to work from Ankara to a hospital in Konya where he worked as a pediatrician. 53-year-old Albayrak was a professor of astronomy at Ankara University and was traveling to a science panel in Konya.

Family, friends and thousands of locals attended the funeral of Adem Yaşar, one of three engineers of the high-speed train, who died in the crash, in his hometown Çankırı, north of Ankara. The father of two was a train engineer for 13 years.

"We wanted him to find an office job in the railroad authority, but he did not want that. He loved his job," his uncle, Mehmet Yaşar, told reporters after the funeral.

Yusuf Yetim, a former bureaucrat who was planning to run for mayor in the upcoming elections in his hometown Bozova in southeastern Turkey, was buried there on Friday.

Funerals will be held for other victims including two engineers and passengers Arif Kahan Ertik, a staff member of the German Ministry of Commerce's Turkey office and Kübra Yılmaz, a biomedical engineer.

Media reports said the absence of a railway signaling system was to blame for the crash, claiming the train and the engine were on the same track for this reason. Authorities detained three railway staff following the incident and are examining the radio communications used by train station personnel and staff on the train. However, Transportation Minister Cahit Turhan said railway signaling systems are not a crucial part of the operation of trains and railways.

"It serves for additional security, to reduce the number of personnel on the ground and for automation. Trains can operate without an automated railway signaling system," Turhan told reporters after attending the funeral of one of victims in Ankara.

The impact of the crash was so severe that media reports initially said a pedestrian overpass collapsed on the train. It was later revealed that the train's cars were launched into the air due to the impact with the railway engine, thus hitting the overpass.

The engine was tasked with checking any problems with the railroad for routine duty, and officials said the crash happened a few minutes after the train left a station in Ankara for Konya.

This is the deadliest train accident since July, when 24 people were killed and hundreds injured after a train derailed in the northwestern province of Tekirdağ. The causes for the derailment were due to ground erosion of the soil under the tracks following heavy rains in the area.

The high-speed train service between the capital Ankara and Konya in the Anatolian heartland was launched in 2011, three years before another high-speed route connecting Ankara and Istanbul. All were parts of Turkey's ambitions to expand and upgrade its railroad network and promote more train trips.

Although they operate at high speeds of up to 250 kilometers per hour, authorities have addressed public concerns on safety, citing a set of measures to prevent accidents including automatic brakes that work when the engineers are incapacitated, a system preventing exceeding speed limits as well as a railway signal system up to world standards that prevents the collision of two trains.