Rostov-On-Don (Russia), Aug 17 (RIA Novosti) At least 20 people were killed and 138 injured Monday in a suicide bomb attack in Russia's southern Ingushetia region, officials said.

A suicide bomber rammed an explosives-laden vehicle into the gates of the police headquarters in the republic's largest city of Nazran. The blast damaged the police building.

The toll could rise as people are still believed to be trapped under the rubbles of the building, officials said.

'The precise number of people who might be under the rubble is not known. We believe there could be some 20 people there. Search efforts are continuing,' an emergencies ministry official said.

He said a fire immediately engulfed the building after the explosion.

He added that 16 injured people are in critical condition.

The explosion left a crater of about four meters wide and two meters deep. The blast triggered more explosions as ammunition detonated in the police headquarters.

The blast shattered windows and smashed balconies in residential buildings within a radius of 500 meters. Some 30 cars parked nearby were destroyed.