A bomb wounded a policeman in a car park outside a police post in the port of Tunis Saturday, a witness and two radio stations said.
The blast hit at 5:45am (04:45 GMT) in La Goulette in the northern outskirts of the Tunisian capital, the witness and Express FM and Shems FM radio stations said.
It occurred as a policeman approached a four-wheel drive vehicle parked in front of the post after garbage collectors spotted a suspicious object underneath it, the witness said.
Residents said they were awoken by the sound of the blast, causing many to panic.
The Tunisian interior ministry could not immediately be reached to confirm the bombing, the first known attack of its kind against a security post in Tunisia.
The blast comes two says after gunmen assassinated opposition leader Mohamed Brahmi, who was to be buried later Saturday amid sometimes violent protests against the government.