MOSCOW (AP) — Russia's foreign ministry says police stopped three American diplomats trying to enter an area of northern Russia where a secrecy-shrouded explosion at a navy range caused a brief spike in radioactivity levels.

Ministry spokeswoman Maria Zakharova said Thursday that the Americans, described as military diplomats, were not held in custody after they were stopped a day earlier.

She told a briefing that the Americans had received permission to travel to the city of Arkhangelsk, but instead went to Severodvinsk, 30 kilometers (20 miles) to the west, where they boarded a commuter train to a community near the naval range. Police informed them they were "in a zone of restricted visitation," she said.

Two servicemen and five nuclear engineers were reported killed in the Aug. 8 explosion.