Azerbaijan's Ministry of Emergency Situations says it is investigating a fire in the Caspian Sea but has received no reports that offshore oil and gas fields are affected.
A strong explosion shook the area on July 4 before photos of the fire appeared on social media.
The ministry said in a statement quoted by RFE/RL's Azerbaijani Service it "has not received any information about any emergencies in the country's offshore oil infrastructure or industrial facilities during the day."
The ministry said it issued the statement "in connection with the video footage of the fire in the sea, which spread (online) on the evening of July 4."
The videos show a large plume of fire, which is clearly visible from Baku.
The ministry said an investigation into the fire was under way.
State oil company SOCAR spokesman Ibrahim Ahmadov was quoted by the Azerbaijani news agency APA as saying the blast took place about 10 kilometers from the Umid gas field, which is 75 kilometers from Baku.
Experts are on their way to the scene aboard a ship, and the public will be informed as soon as there is additional information, Ahmadov said, according to APA.
SOCAR said preliminary information indicated it was a mud volcano, according to the Associated Press. The Caspian Sea has a high concentration of such volcanoes, which spew both mud and flammable gas.
The Ministry of Ecology and Natural Resources said the explosion might have been caused by such an eruption. The ministry and the Republican Seismological Service Center are investigating the explosion, the ministry said.