NEW YORK (AP) — Two large American flags atop the Brooklyn Bridge — one of New York City's most heavily secured landmarks — were replaced sometime during the night with white banners that were spotted Tuesday morning fluttering in the wind.

Police crime scene and intelligence detectives were investigating how the flags were switched out on the famed span that connects Brooklyn and Manhattan, and there were no reports of suspicious activity, police said. Officers in patrol cars are stationed at both ends of the bridge, which is constantly monitored by surveillance cameras.

Investigators are reviewing security footage for clues, police said. The police commissioner was scheduled to brief reporters on the investigation later Tuesday.

More than 120,000 vehicles, 4,000 pedestrians and 3,100 bicyclists cross the Brooklyn Bridge every day, according to the city's Department of Transportation, which maintains the bridge.

Police removed the white flags just before noon from poles on the stone supports that hold cables above the bridge. One of the flags, viewed via video, appeared to have faint traces of stars and stripes on it.

The flags fly from above the pillars year-round and are replaced by DOT workers when they become frayed, police said. They are lit from the bottom by a lamp at the base of each tower at night.