A bomb attack on a military hospital in southern Russia has killed at least 35 people, officials have said. Eyewitnesses say a truck packed with explosives crashed through entrance gates at the hospital, and a driver at the wheel blew himself up. The blast destroyed the four-storey building at a military base in the town of Mozdok, 10 kilometres away from the breakaway Russian province of Chechnya. Medical and rescue teams worked to pull survivors from beneath the rubble, where they could hear people crying out. Eyewitnesses said the truck drove towards the military compound at high speed. "The driver was a middle-aged man. We did not see anyone else inside," one man told the Associated Press. However, other reports said the truck was already parked in the hospital grounds, and possibly set off by remote control. The blast left a crater at least eight meters wide and three meters deep. About 150 people - a mixture of soldiers and civilians - were believed to have been in the hospital at the time of the blast. "Judging by the scale of the destruction and the number of people who were in the hospital... the number of casualties will probably be much higher," Russian deputy general prosecutor Sergei Fridinsky said at the site of the attack. Health authorities in North Ossetia region have made an urgent appeal for people to donate blood. **Security breached*** The region's emergency situations minister Boris Dzgoyev said the hospital building collapsed like "a house of cards" and local police said the building was totally destroyed. The BBC's Sarah Raynsford says questions are already been asked about how this could attack could have happened in one of Russia's most heavily-fortified towns. Russian President Vladimir Putin has sent Defence Minister Sergei Ivanov to the scene of the latest attack. There was no immediate claim of responsibility for the attack. However, Salambek Maigov, Moscow spokesman for rebel Chechen leader Aslan Maskhadov, said the separatist leadership was not involved. "The Chechen presidency is not responsible for terrorist acts and denounces such acts," he told the French news agency, AFP. **PHOTO CAPTION*** Russian Defense Minister Sergei Ivanov. (AFP/File/Kim Jae-Hwan)