Update. The Russian Foreign Ministry told Interfax that American diplomats had informed the Russian Defense Ministry that they would go to Arkhangelsk, not Severodvinsk. According to an informed source, they changed trains several times.
In the Arkhangelsk region, three employees of the American embassy were removed from the train while trying to enter the restricted area without permission.
An informed source told Interfax that the incident occurred on October 14 on a train from Nenoksa to Severodvinsk.
After checking the documents, the diplomats were released.
Among them are the naval attache at the US Embassy Curtis, the attaché at the US Embassy Arriola, and the US military attache Dunn.