A Black Hawk helicopter carrying three Army National Guard members crashed on Thursday in Minnesota during a maintenance test flight, killing everyone on board, Gov. Tim Walz said.

Mr. Walz announced the deaths of the three crew members during a news conference on Thursday night near the crash site.

The names of the victims were being withheld until their family members could be notified, according to the governor, who said that as a retired member of the National Guard, he was particularly affected by the news.

“As governor and as a citizen of this great state, and as a veteran of the Minnesota Army National Guard, my heart breaks for the families, the friends and the fellow soldiers,” Mr. Walz said. “The coming days will be dark and difficult. The state of Minnesota stands ready to assist the families of our fallen heroes.”

The Minnesota National Guard said it lost contact with the UH-60 Black Hawk around 2:05 p.m. local time after the helicopter took off from St. Cloud, Minn.

Officials said, the cause of the accident was under investigation and declined to elaborate on the nature of the maintenance test flight or the age of the helicopter.