Russia's Foreign Ministry says it will issue a formal note of protest to the U.S. Embassy in Moscow after Russian authorities caught three U.S. diplomats in a restricted area near a secret test site in northern Russia, state-run news agency TASS has reported.
The trio, which included the U.S. military and naval attachés, was removed from a train on October 14 and briefly questioned by Russian authorities in the sensitive Arctic shipyard city of Severodvinsk, near the site of a mysterious explosion in August that killed five nuclear workers.
A U.S. State Department spokesman said the diplomats had been on an official trip and that they had notified Russian authorities in advance of their travel plans. The reason for the diplomats' travel was not disclosed.
But Russia's Foreign Ministry said the diplomats had been found in a restricted area more than 40 kilometers from Arkhangelsk, the city they had said they planned to visit.
Interfax said the authorities checked the documents of the three before releasing them.
TASS quoted a source as saying law enforcement authorities suspected the three of breaching rules on foreigners visiting controlled zones.
Interfax quoted the Russian Foreign Ministry as confirming that the diplomats gave notice of their travels, although it said it was for a different destination and that they "probably lost their way."
Severodvinsk is considered to be in a sensitive military region, and foreigners are allowed to visit only under certain conditions -- normally with advanced permission from the authorities.
An explosion on August 8 at the Nyonoksa missile-testing site on the coast of the White Sea, about 50 kilometers from Severodvinsk, killed five people working for Russia's nuclear agency.
A State Department official on October 10 said the United States concluded that the explosion occurred amid an operation to recover a nuclear-powered missile that had apparently crashed during a test.
The blast sent a plume of radiation wafting over the port of Severodvinsk, sending spooked residents rushing to buy up iodine drops from local pharmacies. Iodine is often used as a first resort to protect the thyroid gland from being irradiated in the event of a nuclear incident.
The incident was followed by contradictory statements from local and federal government officials in Russia about the nature of the explosion and the danger it posed to local residents.