Three military men were killed and a fourth injured on Sunday in the third Thai army helicopter crash in little over a week, a force spokesman said. The Bell 212 chopper -- part of the rescue mission following another helicopter crash on Tuesday -- went down in Phetchaburi province, southwest of the capital Bangkok, bringing the death toll from the three incidents to 17. \"There were two pilots and two army technicians on board. One was injured and three were killed,\" Colonel Sunsern Kaewkumnerd told AFP, adding that the cause was not yet clear. Thai television news channels showed aerial shots of the flaming wreckage, in the same jungle-heavy province that witnessed the previous tragedies. The aircraft, which was travelling from Bangkok to a task force base in Phetchaburi, had on Saturday transported bodies from a Black Hawk helicopter crash on Tuesday. Nine people were killed in that chopper crash, as it flew to the site of an earlier crash on July 16, in which five died. Outgoing premier Abhisit Vejjajiva said the two tragedies had a \"great impact\" on army morale.