"The only thing that has changed is its position, and at 0400 Zulu (GMT) ... it was 150 nautical miles (277 km) southeast of the Omani coast, heading toward the Somali coast," a spokeswoman for the Bahrain-based international naval force said.

There has been "no communication with the ship to date," since its hijacking about 220 nautical miles (370 km) east of the Omani coast on Wednesday, she added.

Asked about the potential for a rescue operation, she said that "we consider all options, but at the moment, the situation is just being kept under review."

An official from Enesel, the Greek company that manages the ship, said on Wednesday that the tanker was carrying "about 270,000 metric tons" of Kuwaiti crude, which he said translates to over 1.9 million barrels of oil.

The European Union's Atalanta mission to the seas off Somalia and the Gulf of Aden (EUNAVFOR) said the 319,247-tonne ship is both Greek flagged and owned, and said it was traveling from Fujairah in the United Arab Emirates to Suez when it was hijacked.

"She has a crew of 25 (seven Greek, one Georgian and 17 Filipinos). There is presently no communication with the vessel and no information regarding the condition of the crew," EUNAVFOR said.

Enesel's website says the tanker is 333 metres (1,092 feet) long with a 60-metre (196-foot) beam.

The Piraeus-based shipping company First Navigation Special Maritime Enterprises confirmed its ship had been attacked but had no further comment.

The Irene SL was the second oil tanker to be attacked in that region in two days. On Tuesday, Somali pirates firing small arms and rocket-propelled grenades hijacked an Italian-flagged oil tanker in the Indian Ocean that had been heading from Sudan to Malaysia.

Meanwhile, South Korea’s Foreign Ministry said pirates on Wednesday released a South Korean fishing vessel that was captured nearly four months ago while fishing for crabs.

The ministry said 39 Kenyans, two South Koreans and two Chinese sailors were aboard the Keummi 305. The ship was last reported sailing away from Somalia toward international waters.

A vessel from the EU Naval Force was sailing toward the ship to secure the safety of sailors at the request of a South Korean navy vessel, the ministry said. The 241-ton Kenya-registered trawler was attacked Oct. 9 in the waters off Kenya’s Lamu Island.

No information about a ransom was reported, but pirates only release ships after being paid.

British Royal Navy Lt. Cmdr. Susie Thomson, a spokeswoman for the multinational Task Force 152 based in Bahrain, said that pirates have been waging attacks increasingly deeper into the Gulf of Oman and the Indian Ocean.

Pirates have launched attacks more than 1,000 miles (1,600 km) east of Somalia.