MOGADISHU, Somalia, Oct. 11 - As world powers on Saturday headed toward the Somali coast to end a two-week standoff aboard a Ukrainian ship laden with tanks and weapons, armed pirates hijacked a massive tanker, officials said.

The latest ship to be seized, a Greek vessel flying a Panamanian flag, was traveling from Southeast Asia to Europe, said Noel Choong, head of the International Maritime Bureau's piracy reporting center in Kuala Lumpur, The Associated Press reported.

There were no further details on the ship.

Pirates who have been holding the Ukrainian MV Faina for two weeks have threatened to destroy the vessel unless a ransom is paid. Six U.S. warships are surrounding the Faina and a Russian frigate was heading toward the scene, raising the stakes for a possible commando-style raid on the ship.

There are 20 Ukrainian, Latvian and Russian crew members on board. The ship's Russian captain died of a heart condition soon after the hijacking nearly two weeks ago, officials in Moscow say.

Ukrainian Defense Minister Yuriy Yekhanurov said earlier that Ukraine does not want foreign countries to use power to take the ship. Most of the crew members aboard the Faina are Ukrainian.

Pirates have seized more than two dozen ships this year off the Horn of Africa, but the hijacking of the Faina has drawn the most international concern because of its dangerous cargo — 33 tanks and other heavy weapons.

The threat by the pirates on the Faina was unusual. Pirates operating off Somalia rarely harm their hostages, instead holding out for a ransom that often exceeds $1 million. But international pressure was mounting regarding the Faina hijacking, with NATO forces planning to deploy.

"We held a consultative meeting for more than three hours today and decided to blow up the ship and its cargo — us included — if the ship owners did not meet our ransom demand," Sugule Ali was quoted by AP as saying in an interview by satellite telephone on board the ship late Friday.

He gave the ship owners until Monday night to pay. Ali had said Thursday he was willing to negotiate the ransom demand of $20 million, after nearly two weeks of insisting they would never lower the price.

"Either we achieve our goal and get the ransom or perish along with the ship, its crew and cargo," Ali said.

The U.S. Navy, which has six warships surrounding the Faina off the central coast of Somalia, had no comment on the pirates' threat Friday, said Lt. Nate Christensen, a spokesman for the 5th Fleet, which is based in Bahrain and helps monitor Somalia's coast.

Momentum has been growing for coordinated international action against the pirate menace.

NATO ministers agreed Thursday that they would have seven ships in the area within two weeks. In addition to the six U.S. warships near the Faina, helicopters buzz overhead daily.

Russia also announced it would cooperate with the West in the fight, and several European countries have said they will launch an anti-piracy patrol.

The U.N. Security Council this week called on countries to send naval ships and military aircraft, and U.S. warships are being diverted from counterterrorism duties. (ap/ez)