US investigators were trying to figure out what led a woman with a toddler in her car to ram into a White House barrier before leading police on a high-speed chase which ended with her being shot dead.
Lawmakers and tourists scattered and ducked for cover Thursday as shots rang out during a police operation to halt the woman, who was driving with a one-year-old girl in her black sports car.
Washington police chief Cathy Lanier told reporters the suspect had been pronounced dead, but refused to discuss the driver's possible motive while the investigation was ongoing.
"The child is approximately a year old, and is in good condition, and in protective custody," Lanier said, adding that officers had fired shots at two locations as they tried to halt the vehicle.
A police statement said the car had Connecticut tags. It did not identify the driver.
Two TV stations -- CBS and ABC -- and the Washington Post newspaper identified her as Miriam Carey, from the city of Stamford.
ABC said she was a 34-year-old dental hygienist and suffered from post-partum depression after the birth of her daughter.
"She had post-partum depression after having the baby" last August, said the woman's mother, Idella Carey, ABC reported.
"A few months later, she got sick. She was depressed. ... She was hospitalized," the mother told ABC.
Secret Service spokesman Brian Leary said the motorist was a "black adult female" but that her identity was being withheld until her next of kin could be notified. He also said the young girl was unharmed.
Officials said the chase began at the outer perimeter of the White House security cordon, where the suspect's car struck a barrier and a uniformed Secret Service officer.
At the White House and at the Capitol, the security perimeter worked, Lanier said, adding that a Capitol Police officer and a Secret Service agent had been injured.
"They did exactly what they were supposed to do. They stopped a suspect from breaching the security perimeter in a vehicle at both locations."
No shots were fired at the White House, but agents gave chase. As the car closed in on the Capitol, the seat of Congress, it was cornered by police vehicles and armed officers on foot.
Footage aired by broadcasters showed the woman's car executing a tight U-turn as shots rang out, and then speeding off. Shortly afterwards it hit another barrier and more shots were fired.
Lanier, while refusing to speculate on the cause of the incident, said it "does not appear in any way to be an accident. This was a lengthy pursuit."
It was the second major security breach in the US capital in less than three weeks. On September 16, a deranged gunman stormed the nearby Navy Yard and killed 12 people.
Thursday's scare also came three days into a US government shutdown, which has raised political tensions and caused hundreds of thousands of workers to be sent home without pay.
The chief of the Capitol Police, Kim Dine, said he had no information to suggest a terrorist motive for Thursday's "isolated incident."
David Loewenberg, a 21-year-old student, said he was in his basement apartment near the Capitol when he heard "a succession of seven or eight gun shots" and rushed outside.
"I could make out a black car that had either run up on the side of the curb or crashed," he told AFP, recounting that he saw a police officer leaving the scene "hugging" a child in his arms.
"It was a girl as far as I could tell," Loewenberg said. "The child was taken away pretty quickly by the police officer."
Senators sheltering inside the Capitol told reporters they had heard up to six shots while police sealed off the building and emergency vehicles converged at the scene.
About half an hour after the incident began, the security lockdown at the Capitol was eased and the doors reopened.
Outside the Dirksen office building, which houses senators' offices, staff not sent home by the shutdown could be seen taking cover behind trees and vehicles.
The White House was also briefly placed in lockdown, with Secret Service agents in tactical gear deployed around the building. The security alert was later partially lifted.
Matthew Jacobs, a 26-year-old tourist from Wellington, New Zealand, was on a bicycle near the White House when the car chase began, and said the car tried to ram through a barrier but it "bowled someone over and took off."