TOKYO (Reuters) - A U.S. naval base in western Japan was briefly locked down on Thursday after reports of gunshots, but operations were soon back to normal with no evidence of an active shooter and no casualties, the navy said in an official tweet.

Gunshots had been reported from a building on the base at Sasebo, 980 km (614 miles) west of Tokyo, on Thursday morning, and the base was put on lockdown as a precaution as the building was checked by security, said Darin Wilson, Deputy Public Affairs Officer for U.S. Naval Forces, Japan.

The tweet said that all was clear at Sasebo and the base had returned to normal activities.

U.S. troops have been stationed in Japan since its World War Two defeat. Occasional crime by U.S. personnel or civilian base workers infuriates Japanese people and often fuels calls for the bases to go.