An international armada was preparing to head towards the Somali coast yesterday as the stand-off with pirates holding a Ukrainian ship to ransom threatened to escalate.

Amid warnings that an effective blockade by the pirates could spark a famine in the Horn of Africa, European Union defence ministers meeting in Paris agreed to set up a naval taskforce to tackle the threat.

Two Royal Navy frigates, HMS Chatham and HMS Lancaster, are already in the region and could join the proposed fleet.

The pirates who seized the Ukrainian cargo ship MV Faina were in defiant mood yesterday, vowing to fight if there was an attempt to rescue the crew of 20. They also said that they were only prepared to hand over the cargo of tanks and weapons in return for a ransom of £11 million.

“Anyone who tries to attack us or deceive us will face bad repercussions,” Sugule Ali, a spokesman for the pirates, told the Associated Press in a satellite telephone interview. The vessel is surrounded by half a dozen American warships but no moves have been made to board it.

US military sources said that there was no international legal mandate to take such action, although steps were under way to seek approval from the United Nations.

The World Food Programme says that security against pirates is needed urgently if Somalia is to receive supplies to avert a famine on the scale of the 1980s.

“Plans to beef up the EU's anti-piracy taskforce with several frigates which can escort boats carrying food cannot come too soon,” Peter Goossens, of the World Food Programme for the east African country, said.

The British Ministry of Defence insisted that when the EU force, consisting of ships from ten countries, was established it was not intended to become involved in the MV Faina incident.

The MV Faina, which was captured on September 25, is anchored off the coast of Somalia near the port of Hobyo. The Times learnt that pick-up trucks were seen leaving the Somali capital, Mogadishu, at the weekend in an apparent attempt to unload the arsenal aboard the ship.

The thought of the arms going to Islamist militia may have helped to galvanise Western powers to get tough with the pirates, who have made Somali waters the world's most dangerous.

Bruno Schiemsky, a Somali analyst, said: “The hijacking of this latest Ukrainian vessel has implications for the overall security situation across the entire Horn of Africa.”

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