At least two people were shot at the US Holocaust Memorial Museum in Washington, authorities said today.
Police spokeswoman Traci Hughes said a person walked into the museum with a rifle and shot a guard.
She said the gunman was also shot.
Ms Hughes said their condition was not known. Both were being taken to hospital.
Fire department spokesman Alan Etter told CNN a third person was hurt after being cut by broken glass.
The museum normally has a heavy security presence with guards positioned both inside and outside. All visitors are required to pass through metal detectors at the entrance, and bags are screened.
The museum, located just off the National Mall near the Washington Monument, is a popular tourist attraction. It draws about 1.7 million visitors each year.