A village cash machine has been blown up and a quantity of money stolen.
The explosion happened in the early hours of Monday at the post office in Long Ashton, near Bristol.
Avon and Somerset Police said three people were arrested and are being held on suspicion of causing an explosion with intent to endanger life.
“Cash was taken but it is not yet known how much,” a spokesman said. “Anyone who was in the area at about 03:30 GMT is asked to call police,” he added.