The top naval officer in Britain has warned that fresh intelligence shows that al-Qaeda and other terrorist groups have realised the importance of global maritime trade.
Admiral Sir Alan West said they could launch attacks against merchant ships.
He added that sea-borne terrorism could cripple global trade and have serious knock-on effects for developed economies.
Reports say al-Qaeda member held in UK
Meanwhile, a number of British newspapers have reported that police are holding a senior al-Qaeda operative who was said to be in the final stages of planning a terrorist attack on London's Heathrow Airport.
However, there has been no official confirmation of the story.
The London Times said the man was arrested after a tip-off from Pakistani intelligence, which claimed that he was getting orders direct from Osama bin Laden as head of al-Qaeda operations in Britain.
The paper also quoted Pakistani officials as saying that details about Heathrow were found in the computer of an al-Qaeda member arrested last month in Pakistan. The al-Qaeda operative's job was to send coded messages to al-Qaeda agents worldwide.
The report comes two days after police raids in London and other parts of England in which 13 men in their 20s and 30s were arrested under the Terrorism Act 2000.
One was released without charge yesterday.
