Three workers were killed and another person was injured after a gas leak caused a major explosion in a Russian gas pipeline used to export gas from Siberia to Europe.

The cause of the leak at the Urengoy-Pomari-Uzhhorod line in the Russian Republic of Chuvashia is still unknown, according to the authorities' announcement.

Pictures and video clips taken from the site of the explosion showed a huge ball of flames near the village of Yampakhtino, about 600 km east of Moscow.

There was unspecified work being done on the onshore pipeline, whose construction dates back to the 1980s.

State gas company Gazprom sent an emergency team to carry out repair work.

A specially appointed committee is also scheduled to investigate the cause of the accident, and the local investigation authority has initiated criminal proceedings related to the violation of safety rules.

Several gas leaks occurred in the gas transmission lines from Russia to Europe, as the Baltic Sea waters witnessed a gas leak in 4 different places from the Nord Stream pipeline, according to what the Swedish and Danish governments announced last September.

The Nord Stream pipeline, or the "Northern Stream", is a double pipeline that exceeds 1,200 km in length, and transports gas directly from Russia to Germany via the Baltic Sea, and it is the longest pipeline under sea water.

Supplies through Nord Stream 1 have been suspended since the end of last August for maintenance operations, but the pipeline has not resumed work.