A strong explosion has shaken the Caspian Sea area where Azerbaijan has extensive offshore oil and gas fields, writes The Guardian.

The cause of the blast, which caused a column of fire to rise into the sky late on Sunday, was not immediately determined, but state oil company Socar said preliminary information indicated it was a mud volcano. Socar said none of its platforms were damaged in the explosion.

The Caspian Sea has a high concentration of mud volcanoes, which spew both mud and flammable gas.

Socar spokesman Ibrahim Ahmadov was quoted by the Azerbaijani news agency APA as saying the blast took place about 10km from the Umid gas field, which is 75km off the coast of the capital, Baku.