A package bomb that killed a teenager and wounded a woman Monday in Austin is probably linked to a similar bombing that killed a man elsewhere in the city this month, authorities said, and investigators are considering whether race was a factor because all of the victims were black.

Shortly after Police Chief Brian Manley announced the suspected link between Monday’s blast 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 organizers about additional safety precautions being taken.

🚨If you receive a package that you are not expecting or looks suspicious, DO NOT open it, call 911 immediately. RT- Help us spread this message. 🚨 https://t.co/j9bxbaaBce

— Chief Brian Manley (@chief_manley) March 12, 2018

Four years ago, a driver plowed 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. Monday’s first explosion happened at a home near the city’s Windsor Park neighbourhood and about 12 miles (20 kilometres) from the home where the March 2 package bomb killed 39-year-old Anthony Stephan House. His death was initially investigated as suspicious but is now viewed as a homicide.

Monday’s second explosion — the cause of which was still being investigated — happened in the Montopolis neighbourhood, near the airport and about 5 miles south of the day’s first blast.

Manley said investigators believe the March 2 attack and Monday’s first explosion are related. In both cases, the packages were left overnight on the victims’ doorsteps and were not mailed or sent by a delivery service. He said neither the Postal Service nor private carriers such as UPS or FedEx have any record of delivering the package to the home where Monday’s explosion occurred.

My heart goes out to the family of the individual who died & was injured from the explosion on Old Fort Hill Dr. This type of crime will not be tolerated in #ATX. If you receive a package that you are not expecting or looks suspicious, DO NOT open it, call 911 immediately. pic.twitter.com/sJSYQZMziv

— Chief Brian Manley (@chief_manley) March 12, 2018

“There are similarities that we cannot rule out that these two items are, in fact, related,” Manley said.

Investigators have not determined a motive for the attacks, but it is possible that the victims could have been targeted because of their race, he said.

“We don’t know what the motive behind these may be,” Manley said. “We do know that both of the homes that were the recipients of these packages belong to African-Americans, so we cannot rule out that hate crime is at the core of this.”

Special Agent Michelle Lee, a San Antonio-based spokesman for the FBI, said the agency responded to both events and was assisting Austin police, who were leading the local investigation. She said the Bureau of Alcohol, Tobacco, Firearms and Explosives was leading the federal investigation.

A second package was discovered near the site of the initial Monday explosion and that some residents and media members were evacuated or pushed farther from the blast site as authorities determined whether it was a bomb, Manley said.

Police did not immediately identify the teenager killed Monday. Manley said the woman who was injured in that attack is a 40-year-old woman who remains hospitalized.

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Associated Press Writer David Warren in Dallas contributed to this report.

Will Weissert And Paul J. Weber, The Associated Press