A parcel bomb has exploded at a FedEx depot near San Antonio, Texas, injuring one, the local fire department said.
The incident occurred overnight in the town of Schertz, an hour south of Austin where four bombs have been planted in recent weeks.
No link has yet been established with the previous explosions, which killed two people and which police believe are the work of a serial bomber.
Reports said FBI investigators and a local bomb squad were at the scene.
Three of the four previous devices were hidden in parcels left at residential addresses.
Police said another was probably activated by a tripwire, triggered by two men walking along a street in south-west Austin.>