Deyan Deyanov, 29, has been found guilty by a jury at the Provincial Court in Santa Cruz de Tenerife, Spain, of murdering grandmother Jennifer Mills-Westley, 60, who he decapitated on the holiday island in May 2011.
More top news
The country's top defence officer said the force may ignore any order to launch a nuclear attack which is deemed to be illegal.
Navy officials say they have received seven short satellite calls which are though to have come from the submarine.
The President is to meet with with the army commander who put him under arrest as he resists calls for him to stand down.