MOSCOW, December 10 (RIA Novosti) - Four men who plotted to bomb an express train between Moscow and St. Petersburg were sentenced in Moscow City Court on Monday to 15 to 18 years in a high-security prison.

The four men were detained in July 2011 for planning to blow up a passing Sapsan, an express train linking Russia's two biggest cities, as it traveled through the Moscow satellite city of Khimki.

The trial was closed to the public and most of the documents were classified.

The convicts’ relatives said they would appeal the verdict.

The four men, all of whom were alleged to be adherents of the Caucasian Emirate, a self-proclaimed virtual state entity designated as a terrorist organization in Russia, were arrested with 10 kilograms of explosives, weapons and a map of the site where they had allegedly planned to blow up the train.

At the time Federal Security Service (FSB) head Alexander Bortnikov informed then-President Dmitry Medvedev that a "major act of terrorism" had been prevented, but no further details were provided to the press.

The attack would have echoed a bomb blast two years ago that derailed a luxury Moscow-to-St. Petersburg train, killing 26 people. A North Caucasus Islamist group claimed responsibility for the bombing, saying it was carried out on the orders of its leader, Doku Umarov, one of Russia's most wanted rebels.