An armed woman was arrested outside the White House on Thursday night, a Secret Service official told NBC News. The woman, who was identified as April Lenhart, 23, of Mount Morris, Michigan, was taking part in a demonstration along the north fence line of the White House complex when plainclothes Secret Service agents spotted a holstered handgun on her front hip about 8:28 p.m. ET as President Barack Obama was completing a televised address on immigration inside, the official said.

Lenhart, who isn't cooperating with investigators, was charged with possession of an unregistered firearm, possession of unregistered ammunition and carrying a pistol without a license. A second person who was with her wasn't arrested.

It was the second such arrest in two days. R.J. "Renae" Kapheim, 43, of Davenport, Iowa, was arrested Wednesday near the White House with a rifle and a knife in his car, according to charging documents. Kapheim, who investigators said claimed that President Barack Obama had called him personally for an appointment, pleaded not guilty Thursday to illegally carrying a rifle.

IN-DEPTH

— Kristen Welker and M. Alex Johnson