(CNN) -- A South Korean oil tanker has been hijacked by pirates, the European Union Naval Force Somalia said Monday.
Somali pirates captured the tanker early Sunday about 600 nautical miles (690 miles or 1,111 km) north of the Somali coast, 300 nautical miles (345 miles or 556 km) outside the area in which the EU group operates.
News of the attack came as the Combined Maritime Forces, a cooperative effort by several countries to patrol international waters, warned that pirates in the Somali Basin and the Gulf of Aden are venturing further from their home waters, "revealing their desperation to find easier commercial targets."
South Korea's official news agency, Yonhap, said the 300,000-ton supertanker Samho Dream was on its way from Iraq to the United States, specifically Louisiana. On board were 24 crew members: five South Koreans and 19 Filipinos.
"Ships operating in Somali waters are often accompanied by private or government escorts because of rampant pirate activity in the area, but the ship did not have any guards on board as it was operating in areas where piracy is not frequent," the Yonhap report said.
The South Korean government ordered a Navy destroyer, in the region for anti-piracy efforts, to move toward the tanker's expected route in Somalia waters. But "the main task of the warship is not to intercept the hijacked ship," Yonhap said, citing a Foreign Ministry official.
The government will not negotiate with pirates, the official was quoted as saying. "Samho Shipping will be in charge of any negotiations with the government only playing a supporting role," he said, according to Yonhap.
Valero Energy Corp., the U.S. company that owns the cargo, did not say how much oil was on the ship. But spokesman Bill Day said ships of this size generally carry about 2 million barrels.
At current prices, that cargo could be worth about $170 million.
The Combined Maritime Forces issued a statement Monday praising the success of recent efforts to combat piracy in the area near Somalia, where pirates have ravaged the seas for years to make ransom money.
"The combined efforts of the Combined Maritime Forces (CMF), European Union (EU), and NATO, along with greater use of 'best management practices' within the commercial shipping industry, are having the intended effect, as witnessed by several unsuccessful piracy attempts this past week," the statement said.
"Late March to early April typically marks the beginning of a surge in pirate activity for the months of April and May due to the calming seas off the east coast of Africa, and this year has not been any different. Over the last week there have been 12 unsuccessful attacks and three successful attacks carried out by pirate action groups."
A group of suspected pirates was captured Thursday after attacking a U.S. Navy frigate, the USS Nicholas, in the Indian Ocean.
Also last week, the Sierra Leone-flagged tanker M/V Evita came under attack by three suspected pirate skiffs: smaller boats generally associated with a mother ship. During the attack, the pirates fired rifles and aimed rocket-propelled grenades at the vessel in an attempt to force it to stop, the Combined Maritime Forces statement said. The M/V Evita was able to avoid the attack.
The EU group found the suspected pirates and monitored them as a boarding team entered their skiffs, the statement said.
"After ensuring the suspected pirates had no means to conduct any more attacks, all 11 were released on the two small skiffs, while the mother skiff was destroyed, ending that vessel's ability to engage in any other illegal activity," the statement said.
The Combined Maritime Forces warned that every day, "more young Somali men are taking the risk of life at sea as a pirate. ... It's the same desperation that now leads to numerous pirate action groups spread out all over the Arabian Sea. Now, more than ever, it is crucial that all vessels plying these waters understand that the adoption of best management practices is vital for them to be able to protect themselves."