A suspicious flying object was seen hovering in the sky near the Imperial Palace in Tokyo on Monday night. There were similar sightings last week. Police say the object may have been a drone, even though it is illegal to fly drones in the area.
Police officers spotted the flying object while they were patrolling a park in Chiyoda Ward, near the Palace.
They say the object had flashing white lights.
Officials dispatched a helicopter to the area, and investigators checked to see whether there were any suspicious people in the park.
There have been no reports of objects falling to the ground in the area.
Last Thursday, the day after the Emperor's accession to the throne, unidentified objects, which may have been drones, were spotted in several places in Tokyo.
In Japan, it is prohibited by law to fly drones over crowded urban areas and important facilities, such as the Imperial Palace.