The United Nations has authorised force to free the hijacked Ukrainian ship.

The UN Security Council resolved that states with warships and planes in the area should attack the ship "on the high seas and airspace off the coast of Somalia".

Military experts believed the most likely option was a commando style raid to overpower the pirates on board, rather than a direct attack on the ship.

Shelling the vessel could cause a catastrophic explosion and kill the hostages as well as losing the entire cargo, they said.

The Security Council resolution was described by the UN as necessary to repress piracy, consistent with the 1982 UN Convention on the law of the Sea.

The vote to attack the pirates holding the ship that has been moored off Somalia since September 26 came as the Kenya Government through Foreign Affairs minister Moses Wetang'ula backed the use of force to repossess the ship.

The Government has insisted the controversial 33 T-72 tanks, rocket propelled grenades and spare parts on the MV Faina belong to Kenya's Defence ministry although other reports maintain the cargo was destined for South Sudan.

Approval for force came as a Reuters report quoted an associate of the pirates holding the ship as saying an $8 million (Sh576m) ransom deal was in the offing, which may enable the boat to be freed within days.

"A boat will carry the money from Djibouti and pirates are expected to release the ship in the coming two nights," a business partner of the pirates, who identified himself only as Farah, told Reuters.

"I think the Americans are aware of the deal because there is no other alternative to release the ship," added Farah, who has given reliable information in the past about piracy.

"If the warships threatened, pirates would die in a last-ditch fight and risk the hostages."

Tuesday's UN resolution poses a challenge to Kenya's ability to secure the tanks to which it has laid claim.

Restore order

The 15-country UN Security council has on more than one occasion called for the deployment of military vessels and aircraft to restore order in the lawless Gulf of Aden.

On Wednesday, Mr Wetang'ula said: "We will fight the pirates anywhere and everywhere to keep the high seas safe."

However, the resolution only applies to pirates off Somalia, whose 1,880-mile coastline is the longest in Africa and near key shipping routes that connect the Indian Ocean with the Red Sea.

Addressing a news conference at his office, Mr Wetang'ula insisted that ransom should not be paid. "The more you pay, the more you empower them," he said.

It is estimated that the pirates have made between $30-50 million from ransom payments over the past year.

They have been demanding $20 million to release the ship that was hijacked with arms from Ukraine enroute to Mombasa.

The minister disclosed that the Kenya Navy will patrol Somalia's territorial waters to secure the Indian Ocean coast.

The pirates, he said, were "part of an organised international criminal syndicate" that would have grave consequences on the maritime route to the Mombasa port.

"There is a real risk of merchant ship owners shunning the region," Mr Wetang'ula said.

He insisted that the UN resolution gave "extra-territorial powers", but could not explain if this meant an invasion of Somalia to pursue the pirates on land.

But Somalia's Foreign Affairs minister Ali Ahmed Jama called for caution before using force.

He said that even though the threat "was serious and unacceptable," the safety of crew being held hostage must be taken into consideration.

Mr Wetang'ula also refuted media reports that the arms were destined for Southern Sudan.

He termed the reports as "unhelpful speculation".

Cabinet meeting

Other sources said the issue is likely to be discussed at a Cabinet meeting to be held on Thursday.

Analysts say Southern Sudan could be building up its military power ahead of a 2011 referendum on whether it should secede from the Khartoum Government.

The Faina, captured with 33 T72 tanks and anti-aircraft guns, is moored at the Somalia coast near Hobyo port under surveillance from Kenyan and US forces.