Two men have been injured after an explosion in Austin, Texas, just weeks after two others were killed by parcel bombs in the city.
Sunday's explosion, which has not yet been linked to the earlier ones, occurred around 8.30pm in Travis Country, in the city's southwest.
The men, reportedly in their 20s, were both taken to hospital, where their injuries are not life-threatening.
It is not clear what caused the explosion.
Austin Police Chief Brian Manley said: "We have a scene where it is obvious an explosion has taken place.
"We just simply do not know a lot at this point."
He added: "We want to put out the message that we've been putting out and that is, not only do not touch any packages or anything that looks like a package, do not even go near it at this time.
"We have not had an opportunity to look at this blast site to really determine what has happened."
The explosion is several miles form the city's east side, where three earlier blasts occurred.
These explosions killed two African-American men: Anthony Stephan House, 39, and Draylen Mason, 17.
Mr House was killed on 2 March in an explosion that also damaged a wall and door, while Mr Mason, a young musician, died on 12 March.
Mr Mason's mother was also injured in the same blast.
A 75-year-old Hispanic woman, who has not been publicly named, was hurt in another explosion a few hours later.
She is in hospital.
More than 500 federal agents and Austin Police are searching for the culprits.
Before the latest explosion, police said that the bombings were being looked at as possible hate crimes and that the person responsible appeared to be trying to send a message.
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Mr Manley said: "We are not going to understand that (message) until the suspect or suspects reach out to us to talk to us about what that message was."
Police have received more than 700 calls about suspicious packages since the parcel bomb attacks began and a reward of $115,000 is being offered for information leading to the arrest and conviction of the person or people responsible.