Two package bombs which killed a teenager and wounded two women overnight in Austin are probably linked to a similar bombing that killed a man elsewhere in the city this month, authorities say.
Investigators are considering whether race was a factor because most of the victims were black.
Shortly after Police Chief Brian Manley announced the suspected link between the recent blasts and a March 2 attack that killed a 39-year-old man, authorities rushed to the scene of a third explosion that badly injured a second woman.
Authorities have not said whether that blast was also caused by a package bomb or if the victim, like those hit in the two confirmed bombings, is black.
Austin-Travis County EMS tweeted that the woman is in her 70s and was taken to a hospital with potentially life-threatening injuries.
Authorities urged the public to call police if they receive any unexpected packages.
The latest explosions happened during the South by Southwest music, film and technology festival, which brings about 400,000 visitors to Austin each year.
The explosions happened far from the main events of the festival, and there was no immediate word from organisers about additional safety precautions being taken.
Four years ago, a driver ploughed through a barricade and into festival-goers, killing four people and injuring many others.
Additional security measures were taken in the aftermath, including additional policing, tougher security checks and brighter street lighting, among others.
The three explosions occurred in different parts of east Austin.