Special forces of the Danish Navy warship "Absalon" have stormed a ship captured by Somali pirates and released the 25-man crew - including one Bulgarian - unharmed.

Following a distress call from the captured cargo vessel "Ariella" on Friday morning, an international sea and air response resulting in the boarding of the cargo ship by Danish naval forces, according to EU NAVFOR spokesperson, Commander John Harbour.

Somali pirates had reportedly captured the "Ariella" only a few hours before the distress call was sent.

The elite naval forces had scaled the ship's side, and freed the crew, who had locked themselves in a secure room. Meantime, sailors from the nearby Russian Navy ship Neustrashimyy boarded and detained pirates aboard a second skiff, said NATO spokesman Wolfgang Schmidt.

Some details of the still ongoing operation have remained sketchy. The precise location of the vessel has not been disclosed, but the nationalities of the crew members have been announced, according to FoxNews.

The crew comprised a Bulgarian, a Slovakian, an Indian, 15 Filipinos, and 7 Ukrainians, the EU Naval Force said. They are all said to be safe and well.

This was the first occasion on which a warship that is part of the European Union Naval Force patrol in the Indian Ocean has directly intervened in a hijacking.

"There's been many instances where there's been excellent cooperation and three, four or even five nations have helped deter a pirate attack," Harbour said, adding: "This is the first where a warship has been able to send forces to stop a hijacking while it was in progress."

On this occasion, forces were able to intervene because the ship had registered with naval authorities, was traveling along a recommended transit corridor and was part of a group transit, ensuring the ships had a helicopter within 30 minutes' reaction time, Harbour said.

The 32 000 ton bulk carrier "Ariella" is registered in Antigua and Barbados.

Meantime, the crews of two other vessels, "Asian Glory" and "St James Park", including 13 Bulgarian nationals, remain as hostages to the pirates. On February 3, a record ransom demand for USD 15 M was made for the release of "Asian Glory", with USD 3 M demanded for the other ship and her crew.