WASHINGTON, March 7 (Xinhua) -- The U.S. National Transportation Safety Board (NTSB) announced on Tuesday "a special investigation" of Norfolk Southern Railway's organization and safety culture.

The NTSB urged Norfolk Southern to take immediate action to "review and assess its safety practices," given the number and significance of recent accidents involving the company.

The announcement came more than a month after a Norfolk Southern freight train carrying hazardous materials derailed in East Palestine, Ohio.

The Feb. 3 derailment resulted in a significant fire and hazardous materials release in the area of East Palestine, a village located on Ohio's border with Pennsylvania.

The NTSB said on Tuesday it has launched investigation teams to five "significant" Norfolk Southern accidents, including the East Palestine train derailment, since December 2021.

Earlier in the day, a Norfolk Southern employee was killed during a movement in Cleveland, Ohio.

U.S. Transportation Secretary Pete Buttigieg tweeted in response that several federal agencies "are investigating after a collision this morning killed a Norfolk Southern conductor in Cleveland."

"Our thoughts are with the family facing this preventable tragedy," Buttigieg wrote. "Now more than ever, it is time for stronger freight railroad accountability and safety."