Spanish Prime Minister Pedro Sanchez on Friday acknowledged that "trust in high-speed rail has been shattered" after a deadly accident earlier this week killed at least 69 people and injured 110.
Wednesday's collision near Urda in central Spain was the country's second major high-speed rail disaster this year.
A derailment and collision near the town of Adamuz in January killed 46 people, with preliminary findings pointing to a fractured rail.
"It is unacceptable for a country like Spain, with such a strong high-speed rail system, to suffer two accidents of these characteristics and magnitude in one year," Sanchez said at a press conference.
He pledged to "provide solutions to further strengthen the high-speed rail system so a tragedy of this kind … doesn't happen again."
Spain has the world's second-largest high-speed rail network after China and the largest in Europe, according to the International Union of Railways.
Castile-La Mancha regional President Emiliano Garcia-Page said Friday the death toll could rise slightly as identification work continued. Authorities had received 70 missing-person reports.
Of the 110 people hospitalized in the region, 39 remained admitted, all progressing reasonably well, he said.
Scrutiny is growing over the failures that allowed a Renfe high-speed train to slam into the back of a stationary Iryo train on the Madrid-Seville line.
Transport Minister Oscar Puente said a technical failure in the automatic signaling system halted several trains, prompting controllers in Madrid to take over. Similar glitches have occurred 160 times in Spain this year, Puente said Friday, adding that the figure was within the EU norm.
A worker at the control center then authorized the Renfe train to proceed at normal speed-up to 200 kilometers (124 miles) per hour-despite the stationary train ahead, violating safety protocols, according to Puente.
"If there are two trains in the same block section, the train behind should not move. Second, in these conditions, if the first train moves, the train should be authorized to move at a maximum of 40 kilometers (25 miles) per hour," Puente said.
Around five minutes before the accident, the stationary train had also contacted the control center to warn that it was unable to resume moving.
A preliminary investigation estimated that the Renfe train was traveling at around 160-200 kilometers (99-124 miles) per hour when it struck the stationary train.
The investigation has not established final responsibility, and railway workers and experts have questioned whether the controller's decision, which Puente called "inexplicable," reflects wider weaknesses.
Vicente Almenar, a Renfe train driver with the UGT union, urged caution, warning of intense pressure to speed up operations to prevent delays, Spanish news agency EFE reported.
Antonio Tobal, UGT's safety representative at Adif, cautioned against focusing solely on human error. He called for examining working conditions, organizational procedures and staff training for emergencies.
Other experts have pointed to Spain's rapid high-speed rail expansion and relatively low maintenance spending compared with other European countries. They have also questioned delays in replacing the Madrid-Seville line's aging automatic signaling system with the European Rail Traffic Management System.
Spain's disasters contrast with high-speed rail's strong safety record elsewhere.
Japan's Shinkansen has recorded no passenger deaths from collisions or derailments since services began in 1964.
China's two documented fatal high-speed crashes killed 41 people. France, which has Europe's second-largest high-speed network, has recorded 14 deaths aboard TGV trains in three accidents, including 11 during a test run.
Spain's two crashes this year have killed at least 115 people. Another 80 died in the 2013 Santiago de Compostela derailment.
On Friday, Spain's transport minister rejected calls to resign.
