WASHINGTON, Dec. 5 (Xinhua) -- Three U.S. National Guard soldiers were killed Thursday after a helicopter crashed southwest of the St. Cloud city in northern U.S. state of Minnesota, military authorities said.

The Minnesota National Guard tweeted it lost contact with a UH-60 Black Hawk on Thursday afternoon while the helicopter was conducting a maintenance test flight from St. Cloud.

In another tweet later, the Minnesota National Guard confirmed the deaths of the three personnel on board.

"Our Minnesota National Guard family is devastated by the deaths of these soldiers," said Jon Jensen, the adjutant general of the Minnesota National Guard.

An investigation is underway to determine the cause of the crash, authorities said.