A employee at Department of Energy headquarters in Washington, D.C., has died from COVID-19, Secretary of Energy Dan Brouillette said Tuesday.

News of the he death, the first confirmed COVID-19 fatality at DoE, hit while the agency logged more cases at defense nuclear sites.

“I regret to share with you that we have lost a member of our Forrestal team to COVID-19,” Brouillette wrote in a widely distributed email. “Our teammate fell ill during the second week of March, and had not returned to the workplace since that time.”

The employee who died worked in the Forrestal Building in downtown Washington, Brouillette said. Beyond that, the DoE boss did not provide any details about the deceased, including the person’s job function.

It was not clear that the fatal case reported Tuesday was one of the five confirmed COVID-19 infections the Department of Energy has previously acknowledged at Forrestal. None of those five people left DoE headquarters in the second week of March, according to notices the agency posted online March 18March 30,  and Tuesday.

The DoE press office did not reply to multiple requests for comment seeking clarity. The civilian agency maintains U.S. nuclear warheads and bombs.

In his message to employees, Brouillette called the employee’s death “tragic, and said that it “underscores the need to take care of ourselves and those around us through the precautions we all know well by now.”

More Cases Confirmed at Sites

Separately, three more cases of the respiratory disease have been confirmed this week at DoE’s Savannah River Site in Aiken, S.C. That brings the site’s confirmed total to five, up two from last week’s total.

On the other side of the country, the Sandia National Laboratories said it confirmed another case of COVID-19. The person who tested positive works in the Albuquerque campus’ Environmental Test Lab: Building 860. That brings Sandia’s total confirmed cases to eight from seven last week.

Meanwhile, the Y-12 National Security Complex in Oak Ridge, Tenn., where the DoE makes the uranium-fueled secondary stages of nuclear weapons, is reportedly shifting to minimum safe operations. That means any non-essential employees left on site after Y-12 instituted a mass-telework policy will have to leave. The Bechtel National-led site operations contractor, Consolidated Nuclear Security is continuing nuclear-weapons manufacturing during the transition, which will take about two weeks, a local television station reported.