India said an error in electronic signalling was responsible for the nation’s worst train crash in two decades, which killed more than 300 people on Friday.

The collision, which happened in the eastern state of Odisha, is said to have occurred when a passenger train hit a stationary freight train and ran into another passing passenger train. The trains were carrying 2,296 people in total, the Associated Press reported.

“According to the preliminary findings, there has been some issue with the signalling. We are still waiting for the detailed report from the Commissioner of Railway Safety,” Jaya Varma Sinha from India’s railway board told local media on Sunday.

Prime Minister Narendra Modi’s government has pitched a modernization of the British colonial-era railroad network in India, but despite government efforts to improve safety, several hundred accidents occur every year.

Modi, who called the incident a “painful” one, visited the crash site on Saturday. Anyone found guilty in the incident would be “punished stringently,” he said.

“Words can’t capture my deep sorrow. We stand committed to providing all possible assistance to those affected,” Modi said in a tweet.

EU foreign policy chief Josep Borrell said he was “shocked and saddened” by the accident. “My thoughts are with the victims and their families,” he tweeted.