Deputy Regional Prosecutor Farkhad Saidaliyev told RFE/RL's Kyrgyz Service a criminal case has been opened into the explosion in a building adjacent to the provincial administration headquarters.
Kushbak Tezekbaev, first deputy governor of the Osh region, was in the administration building at the time of the blast. He described the explosion to RFE/RL: "I was in my office. It was about 10 or 15 minutes to 1500 [Bishkek time]. Suddenly there was a huge blast and my room shook. I ran to the corridor and there was smoke. The windows of the third floor were shattered and smoke was coming into the corridor. There was a strange smell. We ran to the ground floor. [It looked like the] windows of the conference building next to the regional administration building had been shattered."
Firefighters were on the scene to extinguish the blaze. No casualties were reported.
Authorities originally believed improper use of a gas canister may have caused the explosion.
The Osh area has seen a number of problems since a revolution in March ousted longtime President Askar Akaev from power.
Protests and riots have threatened stability in the region, which is separated from the capital by high mountains.
(RFE/RL's Kyrgyz Service)