Portuguese police say they seized around 20 metric tons of hashish from a fishing vessel at sea, despite the crew's efforts to sink the ship by exploding a drum of gas as authorities approached.

A police statement Thursday said two crew members were seriously hurt in the explosion and evacuated from the vessel, which was in the Mediterranean.

The statement said the Portuguese Air Force and Navy were involved in tracking the vessel in a months-long operation. Spanish police also took part.

Police said 10 crew of various nationalities were arrested, as well as the suspected leader of the trafficking ring, in Portugal.

The operation was part of an international effort to stop drug smuggling in the area where last year authorities seized 100 metric tons of hashish.