Prime Minister Recep Tayyip Erdogan cancelled a planned trip to Bosnia, scheduled for Friday, to fly to the crash site. Promising a full investigation into the causes of the crash, he described it as a major disaster.
"I express my condolences to the families of the victims," Erdogan said while viewing the site on Thursday.
Many of the 234 passengers and nine crew were trapped in the wreckage after at least four carriages of the crowded Istanbul-Ankara express flew off the track just before 8 o'clock on Thursday night.
Initial media reports said as many as 139 people had been killed, though official figures released by the state's Crisis Management Office later revised this downwards.
Prime Minister Erdogan pledged
a full investigation of the crash
Now, with allegations flying that the train was travelling on track not designed for high-speed trains - and at speeds well above safety limits for the ageing rails - a key part of the investigation already under way will focus on just how fast this Istanbul-Ankara express was going when it left the tracks.
Officials have so far denied that speed was the cause of the accident. Turkish Railways (TCDD) chief Suleyman Karaman told reporters today the express was going at only 75-80km an hour at the time of the derailment.
"This accident shouldn't have happened at this speed. This is not normal," he said.
TCDD officials had earlier said they suspected sabotage, though later backed off this conjecture.
Despite having earlier ruled out negligence, Karaman also announced that the train's chief engineer and two mechanics had been taken into custody for questioning.
Meanwhile, union chief Siddik Aksoy of Hur-Ulasim-Sen, the main rail and transport workers' union, has denied Karaman's claim about the speed of the train. According to Aksoy, the express could have been travelling at a speed of up to 120km per hour when it derailed.
"You cannot have fast trains like these. Our railway lines are not adequate even for speeds of 50kmph, let alone 140kmph"
Siddik Aksoy, chief of Turkey's
main transport workers' union
"The speed had to be more than 120km per house as the last wagon ended up on the top of the first one," he said on Friday.
Aksoy added that as the lines in the region had not been upgraded since 1950, they were not suitable for any trains travelling at more than 50km an hour.
"You cannot have fast trains like these. Our railway lines are not adequate even for speeds of 50 kilometres an hour, let alone 140 kilometres."
Technical experts too had warned that the track being used by the new train - services only started six weeks ago - was unsafe long before Thursday night's accident.
On 10 July, Aydin Erel of Istanbul's Yildiz Technical University called for the high-speed train runs to be halted, warning there was danger due to a failure to upgrade the track.
"I would not get on that train," he said in an article carried in the local media back then. "Despite the train being operational and running, they are only now looking into whether the rail lines are suitable for a fast train. To have that train running now is not appropriate for those railway lines."
Dozens of people were injured
in addition to the 36 who died
Now, there are widespread calls for resignations and criminal prosecutions, with ruling Justice and Development Party (AKP) Transport Minister Binali Yildirim first in the firing line.
"This accident took place despite the warnings of experts," Tuncer Bakirhan, chairman of the pro-Kurdish Democracy Party, said on Friday. "[The accident is] due to officials not taking the necessary measures.
He added: "This incident is evidence that the AKP government does not go to the source of the problem and instead provides showy services - in social issues as well as transport matters. With this many losses, I call on the transport minister and all related officials to resign."
"This incident is evidence that the AKP government does not go to the source of the problem and instead provides showy services - in social
issues as well as transport matters"
Chairman of pro-Kurdish Democracy Party
Opposition leader Deniz Baykal has also called for resignations and a full investigation.
"The government, which acted with negligence and which caused such an accident, would be removed in another country," he said on Thursday night.
The Turkish authorities have also come under fire for clearing the crash site too quickly, before a proper investigation could be carried out. Emin Koramaz, the chairman of the Machine Engineers Association, said the wreckage had been removed without adequate technical investigation.
"There are reports which were submitted to the Transport Ministry and the TCDD ahead of the accident," he said. "These voiced the concern that the route was in no respect suitable for a high-speed train. And in the accident, scientific research was also not given the necessary importance. The political gains were held above science."
The track was declared unsafe
long before Thursday's crash
Another union representative, Fehmi Kutan, the chairman of the United Transport Workers Trade Union, said the AKP wanted to make the railways a domestic political football and this accident was a result of this policy. Incidentally, the high-speed link had been opened amid much much official fanfare.
"This accident is like the murder of 36 people," Kutan said. "The numerous warnings we made on the issue was not taken into account. The TCDD officials closed their ears to the warnings when the high-speed train issue was raised."