(CNN) -- Part of the US Army's Redstone Arsenal post in northern Alabama was on lockdown for hours Tuesday as investigators tried to investigate reports that a shooter was in one of the buildings.
The lockdown remained in effect for the post's Sparkman Center as of about 1 p.m. (2 p.m. ET) -- three hours after the initial alert -- the base in Huntsville said on Twitter.
But a wider initial lockdown, which had included the rest of the post and the neighboring Marshall Space Flight Center, had been lifted, Army spokeswoman Kim Hanson said.
Authorities were "still working on confirming the situation," Hanson said Tuesday afternoon.
Possible active shooter on the Arsenal. Installation is locked down. Run hide fight.
— Redstone Arsenal (@TeamREDSTONE) June 27, 2017
Post spokesman Chris Colster said he still didn't know what, if anything, had happened at Building 5301 -- the Aviation and Missile Command building -- at the Sparkman Center complex, and he had no information about any casualties or anyone put into custody.
"We believe it's a safe situation, and we can allow people to move back around" most of the post, Colster said shortly before 1 p.m.
An Army email sent to facility personnel and relatives shortly after 10 a.m. Tuesday said an active shooter was reported on Building 5301's second floor.
An ambulance service was sent to the facility, said Kristin Clark, a dispatcher for Huntsville Emergency Medical Services.
The FBI said its agents headed to the scene. Base security personnel were working with the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives, Hanson said.
Alabama Gov. Kay Ivey said her office is being updated about the situation.
"I will continue to closely monitor and pray for a peaceful and quick resolution," Ivey said on Twitter.
About Redstone Arsenal
Redstone Arsenal is home to the Army's Material Command and its Aviation and Missile Command.
Redstone has been the center of the Army's missile and rocket programs since the 1950s when it became the home for the contingent of German rocket scientists who surrendered to American forces at the end of World War II.
Civilian rocket research was moved to NASA's Marshall Space Flight Center in 1960.
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