Reading and Chatham letter bombs linked
Anti-terrorism officers believe there is a link between two letter bombs sent to armed forces careers offices in Kent and Berkshire.
The packages were discovered by staff at St Mary's Butts, Reading, and Dock Road in Chatham, on Tuesday.
Police said the packages appeared similar and were being forensically examined after being made safe by bomb disposal experts.
A spokesman said no other devices had been discovered in the mail.
An MoD bomb disposal team was called to the office in Reading at about 14:00 GMT and the area around it was sealed off.
Officers at the scene confirmed it was a "small but viable explosive device" which had been received in the post and had been made safe.
Kent Police said officers were called to the Chatham office at 10:45 GMT following a report of a suspicious package and the scene was declared safe at about 17:00 GMT.