MOSCOW, Nov. 30 (Xinhua) -- The death toll from the derailment of a Russian express train has risen to 26 after an injured woman died in a hospital Sunday night, the Interfax news agency reported Monday.

    A woman that was in critical condition died in the Federal Medical-Biological Center in Moscow Sunday night, Interfax quoted a source in the medical circle as saying.

    Separately, the RIA Novosti news agency quoted an emergencies ministry spokesman as saying that four people remain unaccounted for after the train wreck.

    "The whereabouts of four passengers of the derailed Nevsky Express train have yet to be established," the spokesman said.

    As of Monday morning, over 50 people are still hospitalized, RIA Novosti reported.

    The Nevsky Express, from Moscow en route to St. Petersburg, was derailed Friday night near the town of Bologoye on the border between the Tver and Novgorod regions, some 400 km northwest of Moscow.

    The disaster, which Russian officials say was caused by a homemade bomb equivalent to 7 kg of TNT, is being investigated as a terrorist attack.

    The luxury train carrying more than 600 passengers is popular with business executives and government officials. Among the dead are Boris Yevstratikov, the head of the Russian State Reserves Agency, and Sergei Tarasov, a former senator from St. Petersburg.