DETROIT (AP) — Detroit police say they're investigating a bogus bomb threat that forced the closure of the Ambassador Bridge for several hours, and Michigan Gov. Rick Snyder says the incident shows the need for a second bridge to Canada.

Police say the investigation of Monday night's call continues. No explosives were found in either case.

Detroit police say a 911 call came in around 7:20 p.m. Monday to authorities on the U.S. side of the Ambassador Bridge that links Detroit with Windsor, Ontario.

Just four days earlier, a similar threat was phoned in to Windsor authorities that led to a four-hour closure of the Detroit Windsor Tunnel.

Snyder told reporters in East Lansing says a new crossing "would be helpful" in terms of security. Ambassador Bridge officials oppose building a new bridge.