Athens, March 2 : Greece's Infrastructure and Transport Minister Kostas Karamanlis has resigned following a fatal head-on collision of two trains that occurred in central Greece three days back. At least 36 died in the crash. "It is what I feel my duty to do as a minimal sign of respect to the memory of the people who died so unjustly, taking responsibility for the chronic shortcomings of the Greek state and political system," he said in an e-mailed press statement on Wednesday. "From the bottom of my heart, I once again express my pain and support to the families of the victims," he added. The government has promised a thorough investigation into the causes of one the worst train disasters in the history of Greek railways, according to the Greek national news agency AMNA. Under yet unclarified circumstances near the city of Larissa on Tuesday night, a passenger train travelling from Athens to Thessaloniki, a port city in northern Greece, ended up on the same track with a cargo train that had travelled from Thessaloniki to Athens, the authorities said as quoted by Xinhua news agency report. A search and rescue operation was still underway on Wednesday, focused on the first three carriages of the passenger train that were engulfed in flames after the collision, according to the Greek Fire Service. Based on the findings at the crash site, the death toll will most likely increase further, Greek Fire Service spokesman Vasilios Vathrakogiannis said. At midday on Wednesday, 72 people were still in hospitals, including six in intensive care units, he said. Based on data provided by the Hellenic Train railways operator, there were 342 passengers and 10 employees on board the passenger train and two employees on the freight train when they crashed, he added. Shortly before the Minister's resignation, the train station master in the city of Larissa was arrested, charged with manslaughter through negligence for the tragic train accident, AMNA reported, citing local police. A three-day national mourning has been declared in Greece. /IANS