Al Qaeda has turned its terror sights to the sea, targeting luxury cruise liners in an expansion of its "jihad" against the West.

Owners of the recently launched $1.3 billion Queen Mary 2 (search) yesterday confirmed threats of terror hang over its maiden voyage early next year.

[A spokesman for QM2 owner Cunard (search) told that reports of threats against the ship were unsubstantiated, and that the company was working with authorities on both sides of the Atlantic to monitor the situation.]

The Usama bin Laden terrorist group is also adopting new tactics to destroy commercial aircraft.

British member of Parliament Patrick Mercer (search) has revealed Saudi authorities arrested two Islamic suicide pilots. He said the pilots were preparing to crash two light aircraft into a packed British Airways passenger jet while it was still on the tarmac at the airport in the Saudi capital of Riyadh.

Both light planes had been crammed with explosives. And Italian Prime Minister Silvio Berlusconi (search) said he had received reliable intelligence of a Christmas Day plan to assassinate the Pope and destroy the Vatican by flying a hijacked plane into it.

News of the terror plots emerged after U.S. authorities upgraded their national terror alert status before Christmas.

US intelligence officials also found evidence Al Qaeda was planning to attack the British aircraft carrier Ark Royal as it passed through the Gibraltar Straits en route to the Gulf War earlier this year.

Plans for the attack emerged after a U.S. spy plane discovered scores of acoustic sea-mines had disappeared from a naval base in North Korea.

U.S. intelligence services believe the mines could be aboard 28 "terror ships" Usama bin Laden has assembled in the past year. The capture of Al Qaeda's chief of naval operations, Ahmad Belai al-Neshari, has helped to reveal the extent of the organisation's maritime ambitions.

Al-Neshari was found carrying a 180-page dossier that listed "targets of opportunity". These included large cruise liners sailing from Western ports.

Anti-terrorism expert and former Sydney Olympics security chief Neil Fergus said yesterday that he was not convinced Al Qaeda could launch sea attacks.

"I don't know where Al Qaeda would have got the armada. The Tamil Tigers (search) [separatist fighters in Sri Lanka] have a fleet of about a dozen ships, but they are in an island enclave and that was a difficult exercise," Mr Fergus said.

"I also don't think anyone would have a clue about sea mines from North Korea regardless of U2 flights or satellites."

An Australian aviation industry official said stealing a light aircraft was "as easy as stealing a car if you know what you are doing".

In Australia there have been two recent examples of light planes being stolen — one at Parafield in Adelaide and one in Alice Springs. A light plane was also hijacked in central Queensland.

However the official said it would be "extraordinarily difficult" for a light plane to crash into a large passenger plane due to collision avoidance systems in larger airliners.

A spokesman for the shipping and passenger-ship line P&O last night said exactly the same standard of security for the airline industry was applied for cruise ships.