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.
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".
But he said security officials were "looking very carefully" at whether there was any ongoing safety risk posed by the incident in which all 224 people on board a flight to St Petersburg were killed.
Any change 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's This Morning.
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."
Asked if he would take his own family on a flight to the area, he said: "I would always follow the travel advice and the travel advice is very clear for that part of the world: we don't advise travel to parts of Sinai but actually to Sharm el-Sheikh we haven't changed the travel advice.
"Overall air travel is a very safe form of transport. All the figures back that up and we have a very strong safety culture in terms of airlines."
Mr Cameron said "an enormous effort" went in to cracking terrorist plots to target passenger aircraft.
Russian officials have said the aircraft - an Airbus A321-200 - broke up in the air above the Sinai desert 23 minutes after taking off from the resort.
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.
Alexander Smirnov, the deputy general director of Metrojet, said the cause could not have been a technical fault but "could only have been an external impact on the plane" in mid-air.
There had been no distress call or contact with air traffic control in the run-up to the crash.
The Foreign Office excludes tourist areas along the Nile river such as Luxor, Aswan and the Valley of the Kings as well as the Red Sea Resorts of Sharm El Sheikh and Hurghada from advice against "all but essential travel" to parts of Egypt.
More than 900,000 British nationals visit Egypt every year.