A top Republican politician is in a critical condition after he and three others were shot while practising for a charity baseball game with Democrats near Washington DC.
House of Representatives majority whip Steve Scalise's security guards returned fire and wounded the shooter who was arrested at the scene in Virginia.
All those injured - including the gunman - were taken to hospital before US President Donald Trump announced the gunman had died of his injuries.
A Republican representative said the suspected shooter, named by US officials as James Hodkinson, had asked whether it was Republicans or Democrats who were playing before opening fire.
The shooting is not being treated as an act of terrorism and the investigation has been taken over by the FBI.
Mr Scalise, the number three House Republican leader first elected to the House in 2008, was earlier reported as being in a stable condition having undergone surgery before the hospital updated him to critical.
The 51-year-old's injuries had not thought to be life-threatening prior to the update.
President Trump said he was "deeply saddened by this tragedy" and was monitoring developments, while tweeting Mr Scalise was in his thoughts and prayers.
The shooting occurred at a popular park and baseball complex in Alexandria where politicians and others were gathered for the morning practice at about 7am local time (11am BST).
It came ahead of Thursday's annual baseball game between Democrats and Republicans.
The Republican team was taking part in batting practice when the shots were fired.
Mo Brooks, an Alabama Republican, said he believed Mr Scalise had been shot in the hip and had "crawled into the outfield, leaving a trail of blood" in a bid to get away from the gunman.
Jeff Flake, a Republican who was at the practice, described hearing "a very loud shot" adding: "The gunman was over by the third base dugout with a clear view of the field."
Witnesses reported between 20 and 50 shots being fired that "went on for quite a while".
An earlier statement released on behalf of Mr Scalise said he was in "good spirits" prior to undergoing surgery and that he was "grateful for the brave actions" of all who helped him.
Katie Filous was walking her two dogs near the field where the practice was taking place and said she saw the shooter hit a police officer, who she said was later evacuated by helicopter.
She said the officer had got out of a parked car, drawn a handgun and shouted something to the gunman, who then fired.
Witnesses said as well as Mr Scalise, two police officers and a member of Texas Representative Roger Williams' staff were also shot.