Embassy spokesman Walter Braunohler said there were no fatalities in the incident, which involved a CH-46 Sea Knight helicopter carrying US personnel taking part in the Cobra Gold joint military drills.
A source close to the exercises said two of the helicopter passengers were believed to need emergency surgery, while one sustained more minor injuries and a further three were unhurt.
Cobra Gold is the largest US multilateral exercise in the Asia-Pacific, bringing together thousands of troops from the US, Thailand and other countries for field training.
The annual drills are a key part of the US military relationship with Thailand, whose air bases and ports remain vital to the American military's logistical network in Asia.
Three hurt in US helicopter hard landing in Thailand
Three hurt in US helicopter hard landing in Thailand
BANGKOK: A US Marine helicopter on Wednesday made a 'hard landing' during military exercises in northern Thailand, seriously injuring some of the passengers, the US Embassy in Bangkok said.
Wednesday 20 February 2013 04:08 PM