A Russian submarine broke off a mission in the Black Sea on Saturday and headed back to base, apparently because of engine trouble.

The Alrosa, a diesel-electric submarine, was on a training exercise when the problem occurred, a source in the Black Sea Fleet said, RIA-Novosti reported.

The Black Sea Fleet source said there was no danger to the crew of the Kilo-class vessel, the only operational submarine in the Black Sea Fleet, which is based in the Ukrainian port of Sevastopol. Kilo-class submarines normally carry a crew of about 50 and operate in relatively shallow waters.

A Defense Ministry spokesman told Interfax on Sunday that the Alrosa experienced “several issues in one of the nodes of the propulsion system,” and that it would eventually be returned to service. The Navy could not immediately be reached for comment.

The UNIAN news agency, quoting a Ukrainian military web site, reported that the Alrosa had sent out an SOS message Saturday morning and that three military planes were dispatched to assist. Interfax later denied that report, quoting a Black Sea Fleet source.

Last year, 20 people were killed and 41 injured when fire-suppressant gas was accidentally released on a Russian submarine in the Sea of Japan. It was the country’s worst submarine accident since 118 were killed when the Kursk sank in August 2000.

(Reuters, MT)