BBC has reported that 14 Russian sailors died in a fire aboard a Russian navy research submarine.
The crew were poisoned by fumes as the vessel was taking measurements in Russian territorial waters on Monday.
The ministry gave no details about the type of vessel. But Russian media reports say it was a nuclear mini-submarine used for special operations.
The fire was later put out and the vessel is now at Severomorsk, the main base of the Russian Northern Fleet.
The defence ministry did not say how many crew members were aboard at the time.
An investigation into the incident has begun under the commander-in-chief of the navy.
Russian President Vladimir Putin on Tuesday pulled out of a scheduled event in the Tver region, north-west of Moscow, to discuss the incident with Defence Minister Sergei Shoigu, a Kremlin spokesman said.
Russian news agency RBK cites a military source as saying the vessel was an AS-12 nuclear-powered sub. There has been no official confirmation of this.
The Russian defence ministry has provided few details.
“A fire broke out,” it says, “14 submariners died of smoke inhalation. The cause of the incident is being established.”
The AS-12 is a mini-submarine used for deep water research, intelligence gathering and special operations.
At the same time, there have been multiple reports on Vice President Pence’s airplane being diverted from New Hampshire back to Washington on Tuesday after being called back for an undisclosed emergency.
Pence was scheduled to visit Salem on Tuesday to participate in a roundtable discussion and deliver remarks on the opioid crisis and illegal drug flow in New Hampshire.
But shortly before the vice president was scheduled to arrive, an announcer at the event told the crowd that Air Force Two had been diverted because of an emergency.
“We do have a situation where the vice president was called back to Washington,” Randy Gentry, a representative of Pence’s office, told the crowd, saying the event was being canceled.
A spokesman for Pence’s office said the vice president needs to go back to the White House, and said the vice president will return to New Hampshire at a later date.
President Trump is in Washington on Tuesday, but has no public events scheduled.
Sources at Capitol Hill and the White House could not immediately provide details when asked what type of emergency it entailed.
At same time as these two events occurred, an EU Political and Security Council was taking place.