British experts are meeting to decide whether the Russian airliner crash in Egypt should force any change in UK security plans and travel advice, David Cameron said, amid speculation a bomb may have brought the plane down.
The Prime Minister said people should not stop flying to the popular Red Sea resort of Sharm el-Sheikh despite claims by airline Metrojet that its aircraft was brought down by an "external impact".
Investigations continue into what caused the Airbus A321-200 to crash into the Sinai desert on Saturday, killing all 224 people on board.
British military analyst Paul Beaver said he thought the crash was most likely caused by a bomb on board. He said he was certain Islamic State - who initially claimed responsibility for the crash - do not possess a missile system capable of hitting the plane.
He said: "I'm pretty convinced that Isis (IS) doesn't have a 'double-digit' SAM (surface-to-air missile) that is necessary to go up as far as 31,000 feet.
"That's a very serious piece of equipment, and I don't think they have that sophistication."
He also said the Sinai desert is well-scrutinised by intelligence agencies, so a missile would have been seen.
His comments came after Alexander Smirnov, the deputy general director of Russian airline Kogalymavia - also known as Metrojet - ruled out a technical fault with the plane. There had been no distress call or contact with air traffic control in the run-up to the crash, he said.
Speaking at a news conference, he said: "There are no such things as engine failure or other defects that could lead to an aircraft breaking apart in mid-air.
"Sometimes a few system failures and additional factors could end in a crash.
"But the damage would be during impact on the ground and not in mid-air. In theory, it is possible that it could break apart after an overloading.
"But there are safety systems that would prevent airplanes from going (in the air) under huge pressure. And the only reasonable explanation was that it was some external influence."
Mr Cameron said security officials were "looking very carefully" at whether there was any ongoing safety risk posed by the incident.
Around 900,000 Britons visit Egypt every year, and any change about security information would not be based on "speculation" about the causes, he added.
"There is a meeting taking place right now to try to find out everything that we know and if it's not safe - if certain routes aren't safe or certain things aren't safe - of course we will act," he told ITV.
Mr Cameron, who spoke yesterday with Russian president Vladimir Putin about the crash, added: "If anything changes, we don't sit around and chew our pens and not act. If anything changes it will be announced very quickly.
"But as I say we must do it on the basis of evidence and not on speculation."
Emergency workers and aviation experts continue to comb debris spread over a wide area for clues and the black box flight recorders are said to have been recovered in good condition.