The ban would apply to all fishing trawlers and vessels would need written permission from navy chief Wasantha Karannagoda to enter the prohibited zone, the official said.
"The move follows the attack against the navy and this is being done to prevent a recurrence of what we experienced on Saturday," the official said on condition of anonymity.
The navy said Tiger rebels detonated an explosives-laden trawler in a suicide attack as the gunboat approached for an inspection.
The rebels have not officially commented on the attack.
The new ban comes two weeks after President Mahinda Rajapakse eased fishing restrictions, citing an improvement in the overall security situation in the troubled region.
However, Scandinavians monitoring a tenuous truce between Colombo and the rebel Liberation Tigers of Tamil Eelam (LTTE) said Sunday that tensions were rising.
The Norwegian-led Sri Lanka Monitoring Mission (SLMM) said they could not accept a denial by the LTTE of involvement in Saturday's atta