A driver rammed a car into two Capitol Police officers at a barricade outside the US Capitol in Washington on Friday afternoon, killing one and injuring the other.
The suspect, who got out of the vehicle wielding a knife, was shot dead by police.
The Capitol and surrounding roads were temporarily blocked following the incident. Police say the attack is unlikely to be related to terrorism.
Security had been tightened at the Capitol after a siege in early January, but the measures were recently eased.