Alfredo Perez Rubalcaba said that the ETA's statement on Sunday fell short of what Basque society and other Spaniards demand from the militant group, which is that it renounce violence for good.
The minister told Spanish National Television Monday he is convinced ETA will continue with other illegal activities like trying to amass weapons.
Rubalcaba said the militant group declared the truce because it is so weak it cannot stage attacks.
Its last deadly attack in Spain was in July of last year, when it killed two policemen with a car bomb. Nearly 240 of its members have been arrested since 2008.