According to the police, the Americans were heading to Mannar after visiting the Norocholai coal power plant when the accident occurred.
The vehicle they were travelling in had veered off the road and fallen off the bridge and into a river injuring all three of them.
The police said that the Americans were admitted to hospital for treatment.
The vehicle had sunk some 10 feet in the river and attempts are being made to lift the vehicle out.
Investigations into the accident are underway.