A car bomb has exploded near the University of Navarre in the northern Spanish city of Pamplona.
At least 15 people have been caught up in the blast. The extent of their injuries is unclear but several were hurt by flying glass and debris.
Police reportedly received a telephone call from a person speaking in the name of ETA one hour before warning of a car bomb in the University, without specifying where it was.
The explosion took place in a car park next to the student campus with several vehicles bursting into flames.
The blast comes two days after Police arrested 4 members of a suspected commado unit of the armed Basque group ETA early on Tuesday morning.
Three of the suspects were arrested in Pamplona with the other arrest coming in Valencia. Police say they seized several arms and explosives during the early morning raids.
ETA is blamed for more than 800 killings in its four decade fight for Basque independence.
The group has been responsible for 5 deaths since breaking its declared ceasefire in June 2007.
The European Union and the United States list ETA as a terrorist group.