MOSCOW — The Russian authorities removed three American diplomats from a train heading to an Arctic town near the site of a recent nuclear accident, Russian news agencies reported on Wednesday.

The removal occurred on Monday in the shipyard town of Severodvinsk, according to Interfax, a Russian news agency. The diplomats were about to take a train to Nenoksa, the village closest to the military testing site where a mysterious explosion in August left seven people dead and caused a spike in radiation levels miles away.

Both Nenoksa and Severodvinsk, which stand about 25 miles apart, are closed cities that require foreigners to obtain a special permit from the authorities before arriving. Russians must also gain special approval to enter Nenoksa.

A State Department spokesperson said in an email on Wednesday that the American diplomats “were on official travel and had properly notified Russian authorities of their travel.”