Detroit •A bogus bomb threat forced the closure of the Ambassador Bridge for several hours, the second such threat to a major crossing connecting Detroit to Canada in recent days.

Detroit police said 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. The caller said a bomb would go off in 10 minutes along the busy freight crossing, police Inspector Don Johnson said during a news conference Monday night.

The call prompted authorities in both cities to halt all truck and car traffic across the bridge, said Detroit police spokeswoman Sgt. Eren Stephens.

The bridge was reopened around 1 a.m. Tuesday after security sweeps failed to turn up any incendiary devices, Stephens said.

Traffic was backed up when the bridge re-opened early Tuesday, but was clear by rush hour, according to the Michigan Department of Transportation.

Just four days earlier, a similar threat was phoned in to Windsor authorities that lead to a four-hour closure of the Detroit Windsor Tunnel, a busy border crossing beneath the Detroit River connecting the two border cities. No explosives were found.

At the time, police said a man had called from a street pay phone and warned of a bomb on the Canadian side of the tunnel. Authorities have since said surveillance video from a coffee shop near the phone booth where the call was made might offer clues about the caller.

Johnson said the call Monday came in from somewhere in Detroit, though other details weren't immediately released.

Police had set up several roadblocks near the bridge, where canine units were called in to search the bridge. The Coast Guard was patrolling the Detroit River beneath the bridge and blocked river traffic until about 1 a.m. Tuesday as well.

The closing led to major traffic backups on expressways and other major roads leading into downtown Detroit, Stephens said. Car and light truck traffic was being diverted to the Detroit Windsor Tunnel about 2 miles away, though large trucks cannot use the underwater commuter tunnel.