Police in Texas have issued an alert to the public after two package bombs a few miles apart killed a teenager and wounded two women on Monday, in Austin, and may be linked to a similar bombing that killed a man elsewhere in the city earlier this month.

Investigators are considering whether race was a factor because all of the victims were minorities. Three of the victims were black and a woman wounded in the second blast on Monday was Hispanic, police said.

Shortly after the police chief, Brian Manley, held a news conference in which he linked the attack with a 2 March attack that killed a 39-year-old man, authorities rushed to the scene of a third blast, which badly injured a woman.

Speaking again on Monday afternoon after the third blast, Manley said: “Similar to the other two incidents, the victim in this incident came outside of her residence and found a package out front and she picked up that package and at that point the explosion, the bomb, detonated.”

Authorities have urged the public to call police if they receive any unexpected packages.

The explosions happened with hundreds of thousands of visitors in the city for the South by Southwest festival. The blasts took place far from the festival’s events, and there was no immediate word from organizers about additional safety precautions.

The three explosions occurred in different parts of east Austin. Monday’s first explosion happened 12 miles from the home where the 2 March package bomb killed Anthony Stephan House.

Monday’s second explosion occurred about five miles south of the day’s first blast.

In Monday’s first attack and the attack on 2 March, the packages were left overnight on the victims’ doorsteps and were not mailed or sent by a delivery service. Manley said the US Postal Service did not have a record of delivering the package to the home where Monday’s explosion occurred, and that private carriers like UPS and FedEx also indicated that they had none.

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

Manley said investigators haven’t determined a motive for the attacks, but it is possible that the victims could have been targeted because they are black.

“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. But we’re not saying that that’s the cause as well.”

The 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 taking the lead on investigating. She said the Bureau of Alcohol, Tobacco, Firearms and Explosives was taking the lead on the federal investigation.

Manley said that 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.

Police didn’t immediately identify the teenager killed on Monday. Manley said the woman who was injured in that attack was a 40-year-old woman who remained hospitalized.