A bomb exploded near a police post in the port of Tunis on Saturday, damaging a police vehicle, the interior ministry said.
The blast, the first known attack of its kind against a security vehicle in Tunisia, came just hours before the funeral of assassinated opposition leader Mohamed Brahmi.
A resident of La Goulette, in the northern outskirts of the Tunisian capital, said that the 5:45 am (0445 GMT) blast slightly wounded a policeman but ministry spokesman Mohamed Ali Aroui said no one was hurt.
"An improvised bomb went of on Habib Bourguiba Avenue in La Goulette damaging the back of a National Guard vehicle but causing no casualties," Aroui told AFP.
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The witness said a policeman was hurt as he approached the four-wheel drive vehicle parked in front of the police post after garbage collectors spotted a suspicious object underneath it.
"The explosion caused minor injuries to a policeman stationed at the National Guard post," the witness said.
Residents said they were awoken by the sound of the blast, causing many of them to panic.
The blast came two days after gunmen assassinated Brahmi outside his home using the same weapon used to gun down fellow opposition politician Chokri Belaid in February, according to Interior Minister Lotfi Ben Jeddou.