An explosion has injured two people in Austin, Texas, following a deadly series of bomb attacks in the city.
Three parcel bombs left on doorsteps have killed two people and injured two others since early March.
Police have not confirmed whether Sunday night’s incident is linked to the attacks, but have told residents to remain indoors until the area is safe.
The latest blast came hours after officials announced a new $100,000 (£71,000) reward for information.
The cash reward is on top of an existing $15,000 being offered by the state’s governor.
Both of the men killed earlier this month were African Americans and police have not ruled out racism as a possible motive.
Austin police chief Brian Manley told reporters he believed the attacks were “meant to send a message”.
He said authorities could not confirm whether a specific ideology was behind the attacks, but appealed to those behind the bombings to contact authorities directly.
Mr Manley re-issued a warning to the public to not touch any packages they were not expecting.
“Not a single one of these bombs has exploded without being handled,” he said.
Hundreds of federal agents are helping local police, but there has been no arrest. Authorities say they have responded to 735 reports of suspicious items since last Monday.
The first bomb exploded on 2 March, killing Anthony Stephan House, 29, at his home. Two more bombs exploded 10 days later, and were linked to the initial blast.
Draylen William Mason, 17, was killed when he brought a package inside his home. The explosion also critically injured his mother.
Hours later a 75-year-old Hispanic woman was injured by another package. Local media reports this may have been intended for someone else.
The local National Association for the Advancement of Colored People (NAACP) president Nelson Linder told NBC news that the two murdered victims had links to local prominent African-American families and were connected by the same Methodist church.
Investigators say the devices were being left on doorsteps overnight, not being delivered by official methods.
With the city on high alert, a concert by hip-hop band the Roots was cancelled on Saturday after organisers received a bomb threat via e-mail.
They were due to perform at the city’s South by Southwest festival, known as SXSW.
A 26-year-old was later arrested, but police have ruled out any link to the package bombs.
BBC