CAMP FOSTER, Okinawa — Four Marines remain hospitalized Thursday following a hard landing by a Sea Knight helicopter during a joint exercise in Thailand, the Marine Corps said.

The Marines, who are with the Marine Medium Helicopter Squadron 262 of the 31st Marine Expeditionary Unit based in Okinawa, are being treated for non-life-threatening injuries at a hospital near Phitsanulok, Thailand, according to spokesman 1st Lt. Gregory Carroll. The service did not release the names of those injured.

The CH-46E helicopter had seven Marines aboard when it went down during routine midday flight operations Wednesday as part of the annual Cobra Gold exercise, which is sponsored by the United States and Thailand. There were no fatalities.

The incident is under investigation, Carroll wrote in an email to Stars and Stripes.