The commander of the Estonia Navy has resigned after customs officials said they found smuggled alcohol and cigarettes aboard an Estonian ship taking part in NATO operations on the Baltic Sea.

The Defense Ministry said Wednesday that Captain Sten Sepper took full responsibility for the 56 cases of undeclared cigarettes and 1,000 liters of undeclared liquor customs officials seized from aboard the Estonian minehunter Sakala earlier this month.

Sepper tendered his resignation to Defense Minister Hannes Hanso, who described the incident as "unacceptable."

The Sakala's commander, Lt. Cmdr. Ott Laanemets, also announced his resignation.

Authorities haven't released details on where the contraband was picked up or where it was being taken. A criminal investigation has been launched.