A suicide truck-bomber rammed into a gate outside a dormitory housing Russian anti-riot police early Monday, killing at least 54 and wounding more than 100 in one of the deadliest attacks yet on Russian forces in the secessionist region of Chechnya. The blast in Argun, east of the war-ruined capital, Grozny, was one of five suicide truck bombs sent against Russian targets late Sunday and early Monday. Most of the trucks were stopped at checkpoints late Sunday and then exploded, with some casualties, including the drivers. Russian officials said at least 37 Russian servicemen, 11 civilians and six rebels were killed in Monday's blasts. In addition, four Russian servicemen were missing as rubble was still being cleared from the Argun site, and more than 100 were injured. The coordinated bomb attacks highlighted the tenuousness of Russia's grip on the separatist region despite Moscow's recent declarations that the war is over. In fact, the conflict has largely shifted from battlefield combat to a guerrilla war. The Chechen fighters have returned to mountain ambushes and hit-and-run tactics that they used from 1994 through 1996, when they ousted Russian troops from the region. Russian forces took back most of Chechnya in a military offensive beginning last autumn. "We have two Chechen battalions of suicide-bombers, 500 people, who are ready to die for Islam," rebel spokesman Movladi Udugov said after the attacks. "This is the start of the first phase of our large-scale operation to free Chechen villages and destroy the Russian aggressors." About 5 a.m. Monday, the Argun truck bomber drove close to a lightly protected two-story building housing the police detachment, which normally is based in the city of Chelyabinsk, in the Urals. The dormitory was vulnerable, according to Russian spokesman Sergei Yastrzhembsky, because there were no concrete barriers around it. Police fired at the truck as it approached and it exploded. The blast dug a crater 16 feet deep and 32 feet wide, and destroyed two buildings, Russian news agencies said. Many of those killed apparently were crushed by falling concrete walls. Vasara Vesitaya, a worker in the dormitory cafeteria, left for home three minutes before the blast. "I left the fence and suddenly saw a huge truck coming at high speed. It crashed through the barrier and then something horrible began. The glass from windows in surrounding houses shattered, the earth shook," she said. Gen. Valery Manilov, deputy chief of the general staff, told Russian television that orders to protect military areas with perimeter defenses and checkpoints "have not been fulfilled completely." But the Interfax news agency quoted witnesses as saying the truck that exploded in Argun managed to approach the dormitory because it was already in the town and didn't have to pass any checkpoints. Russian authorities were quoted as saying the truck carried 1,100 pounds of explosive. Truck parts were thrown hundreds of feet by the blast. Yastrzhembsky said that the suicide missions were all carried out in a similar manner, with heavy trucks laden with explosives, and that the targets were "meaningful figures" in the Russian military command and among the Russian authorities. The other servicemen and civilians were killed in two truck bombings and an ensuing shootout in Gudermes, one truck blast in Urus-Martan, south of Grozny, and one truck blast in Novogrozny, in eastern Chechnya. All are in territory the Russians ostensibly control. Security agents detained 18 people on suspicion of involvement in the rapid succession of five bombings, Deputy Interior Minister Ivan Golubev said. Russian officials say some rebels have hidden among civilians and are using weapons caches hidden in Russian-held territory. But others blamed a lack of discipline among Russian troops, including heavy drinking and bribe-taking. Defense Minister Igor Sergeyev urged "improving discipline and diligence in the federal forces."