A National Court spokesman said Monday the six are charged with piracy, weapon possession and membership of a criminal group.
The six were arrested in January 2012 following a shootout when they allegedly tried to board the Patino vessel. The Defense Ministry said the attackers possibly mistook the warship for a freighter.
The six claim they are fishermen and had approached the ship for help.
The Patino formed part of a European Union flotilla fighting piracy in the Indian Ocean.
The trial is expected to end Wednesday.
The official spoke on condition of anonymity because of court rules.
Press; By CIARAN GILES]
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