Security has been stepped up on the QE2 in Alexandria, Egypt, after an unspecified threat, the cruise liner's owners Cunard have confirmed.
The QE2 is set to celebrate its 40th birthday next year
The firm said it had put the vessel on a higher level of security after receiving "certain information".
The QE2, which is on a 109-day world cruise which started from Southampton on 3 January, currently has about 1,700 passengers on board.
Cunard said all passenger excursions from the vessel were going ahead.
"We believe there is no cause for alarm," said Cunard spokeswoman Julie Benson.
"As a precaution, we have placed the ship on to a higher level of security as it passes through this area."
Police boats tracked the QE2 as it sailed northwards through the Suez Canal on Tuesday and stood guard when it berthed in Alexandria the following day.
The city is about a three hours' drive from the pyramids near Cairo.
The UK Department for Transport said it was aware of "some information concerning the security of the QE2".
A spokesperson added: "We treat all such information very seriously and we have acted upon it.
"We are in contact with the operator of the ship and are continuing to monitor the situation carefully."
The QE2's next port of call is Kusadasi in Turkey.
The 67,000-ton vessel, launched in 1967, gave up its Cunard Line flagship status to newer sister ship the Queen Mary 2 last year.