Washington  - The seizure of a vessel last week off the coast of Somalia reflects the region's rising piracy problem, which could require greater security measures to ensure the safe flow of cargo, the US Defence Department said Tuesday.

"This is a persistent problem, although an increasing one, that has indeed drawn the attention of high-ranking people within this building," Pentagon spokesman Geoff Morrell said.

Pirates on Thursday took control of a Kenya-bound cargo ship carrying 33 Russian-built T-72 tanks, armoured personnel carriers and munitions and are holding the 20-member crew hostage.

US Navy warships have moved in and are monitoring the MV Faina, based out of Ukraine, to guard against the possibility that the pirates could attempt to deliver the ship's cargo to terrorists.

"What we're concerned about now is, it's not in the control of those people who intended to deliver it to the government of Kenya," Morrell said. "It's now in the control of pirates, to whom we do not know they will sell this material - and that's what's of concern."

The pirates are demanding a 20-million-dollar ransom for the crew and have said everyone on board will die if an assault is launched against the MV Faina.

Morrell said the United States does not support paying a ransom.

"Obviously, we do not believe in paying terrorists," he said. "I don't believe we believe in paying pirates."

The US Fifth Fleet, based in Manama, Bahrain, is overseeing US operations to monitor the MV Faina but is not involved in negotiations with the pirates, Morrell said.

He could not confirm reports that disagreements among the pirates resulted in a firefight that left three of them dead.

Andrew Mwangura of the East African Seafarers' Assistance Programme told Deutsche Presse-Agentur dpa that the pirates got into a dispute over whether to abandon the heist after international warships arrived on the scene.

"Some of them want to bail out or abandon the mission, and others are ready to continue," Mwangura said.

The US Fifth Fleet, citing rising piracy, announced plans in August to increase coordination with other countries to broaden security along sea routes off the Horn of Africa. (dpa)