Moscow, 10 September 1999 (RFE/RL) -- The death toll from a blast in a Moscow apartment building has already surpassed 60 and is expected to continue to rise as another 40 people are feared still buried under the rubble. Rescue workers toiling through the night say they have little hope of finding any more survivors. The causes of the blast which ripped through the nine-storey building early yesterday are still not clear. Russian officials now say it was most likely triggered by an explosive device. A spokesman of the Federal Security Service (FSB) dismissed earlier suggestions a gas leak was to blame but declined to say whether the explosive responsible was part of a bomb or was stored in the block and detonated accidentally. The FSB also said it had already identified suspects and made sketches of them. Moscow Mayor Yuri Luzhkov, returning to the scene of the blast early today, said the explosion had originated in a ground floor flat rented by a private company. Police have stepped up security throughout the Russian capital. Yesterday's blast came less than two weeks after another blast at a Moscow shopping mall and four days after a massive car bomb attack in a Dagestani city killed 64 people.