ATHENS, Greece - A Greek navy minesweeper and a Portuguese-flagged cargo ship collided Tuesday outside Greece's main port of Piraeus, leaving two navy crew slightly injured and prompting the evacuation of the severely damaged military vessel.

It was not immediately clear why the navy ship Kallisto and the Maersk Launceston container vessel, which had been heading to Turkey with 22 crew on board, collided.

The coast guard said a rescue operation was launched with three coast guard patrol boats, a coast guard special forces unit, a navy ship and helicopter and four tug boats. All 27 navy crew members were rescued from the minesweeper, which sustained damage and was taking on water.

The container ship's managers, J.T. Essberger, said the ship's crew participated in the rescue operation. In a statement, the company said there were no injuries on board the cargo ship, and an initial assessment did not indicate any damage.

The Kallisto, listing to one side and with severe damage to its stern, much of which appeared to be missing, was towed to a naval base on the nearby island of Salamina. The ship is a British-built mine countermeasures vessel capable of sweeping and hunting mines.

The two injured crew members were transported to a hospital, while the rest were transferred to another navy vessel, the coast guard said.

The container ship's managers said the coast guard “have been conducting preliminary interviews with the crew of the Maersk Launceston. A full investigation will follow.”

Greek authorities have barred the cargo ship from setting sail.