MAGAS, Russia - A truck filled with explosives blew up Monday outside a government security building in a southern Russian region bordering Chechnya, killing at least three people and wounding at least 17, an official said.

The explosion shattered all the glass in the Ingushetia regional headquarters of the Federal Security Service, or FSB, leaving the three-story building severely damaged but still standing. The ITAR-Tass news agency reported that there were as many as 100 people in the building at the time of the blast.

Overturned cars lay crumpled in a pile near the charred FSB building in Ingushetia's capital, Magas. An Associated Press reporter saw at least one dead body inside one of the cars.

No group immediately claimed responsibility for the bombing, but the Federal Security Service had been leading the Russian campaign against Chechen rebels. It recently handed control over to the Interior Ministry - a shift officials called a sign that situation in Chechnya was becoming more stable.

The force of the blast was so great, said Muslim Dudarov, a man who works in a nearby building, that he was thrown out of his office and into the building's lobby. He said that numerous people were hit by flying glass.

Abukar Gostoiyev, a deputy security minister in Ingushetia, said three people were killed and 17 hospitalized with injuries. He said that preliminary information indicated that the truck was parked when it blew up and that there was nobody inside it at the time.

An Emergency Situations official at the scene, who declined to give his name, said three people died after being transported to the hospital and a fourth body was found at the site. The ITAR-Tass news agency reported that four were dead and about 40 injured.

Viktor Shkareda, a deputy chief of the Emergency Situations Ministry's southern Russia branch, put the death toll at two. He said that 22 were injured, four in critical condition. It was not immediately possible to reconcile the conflicting death tolls.

Russia has been wracked in recent months by bombings, most of which the government has blamed on Chechens.

A series of suicide bombings and other attacks in and around Chechnya and in Moscow has killed more than 150 people in the past five months. On Aug. 1, a truck packed with explosives rammed through the gates of a military hospital in North Ossetia, which borders Chechnya and Ingushetia, blowing up and killing 50 people.

The nation had been on high alert amid fears that rebels would try to stage an attack ahead of Chechnya's Oct. 5 presidential election, a vote that Russian President Vladimir Putin has said is a key step on the road to peace.