A man found parked with an AR-15 near the U.S. Capitol in Washington, D.C., was arrested Tuesday afternoon. 

"USCP Officers just arrested a man with a gun in the park across from Union Station," U.S. Capitol Police wrote on X just before 1 p.m. local time. "At this time we have no reason to believe there is an ongoing threat. We are working to gather more information and will put out more details when they are confirmed." 

Capitol Police confirmed to Fox News that the gun was an AR-15, and the man has been arrested. Authorities believe he was acting alone. 

The department had sent out an alert that Capitol police was responding to a suspicious package in the Upper Senate Park.

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"Staff and other personnel are directed to AVOID THIS AREA until further notice. Updates will be provided when available," the alert had stated.

With the suspect in custody, police said the investigation is ongoing, but the area of the park has since been secured.

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"We just searched the area in the park that we secured. Out of an abundance of caution, [we're] going to search the suspect’s belongings. Again, the suspect is in custody. Investigation ongoing," Capitol Police added on X. 

Police announced road closures along Columbus Circle between Louisiana and Delaware Avenues, NE and D Street between Louisiana and Delaware Avenues, NE due to police activity. 

In an update just before 2 p.m., Capitol Police wrote on X, "Still investigating. Keep you all posted when the scene is clear. Again, the suspect is in custody. Thanks for your patience as we work to confirm all the information."

This is a breaking news story. Check back for updates. Fox News' Alexandra Rago, Chad Pergram and Kelly Phares contributed to this report.