Meanwhile, Russian and Egyptian investigators said Wednesday that the cockpit voice recorder of the Metrojet Airbus 321-200 had suffered substantial damage in the weekend crash that killed 224 people. Information from the flight data recorder has been successfully copied and handed over to investigators, the Russians added.
Prime Minister David Cameron's office said British aviation experts were headed to the Red Sea resort of Sharm el-Sheikh, where the flight originated, to assess security before British flights there would be allowed to resume.
No British flights were flying to the resort Wednesday, but several were scheduled to depart.
Cameron's 10 Downing St. office said late Wednesday that the team's preliminary report "noted that the Egyptian authorities had stepped up their efforts but that more remains to be done."
Cameron's 10 Downing St. office said in a statement that it could not say "categorically" why the Russian jet had crashed.
"But as more information has come to light, we have become concerned that the plane may well have been brought down by an explosive device," it said.
Downing St. said Cameron had discussed the issue of security at the Sharm el-Sheikh airport with Egyptian President Abdel-Fattah el-Sissi, who flew to Britain on Wednesday for an official visit.
The British disclosures would be an embarrassment to Sissi, who had insisted in an interview with the BBC on Tuesday that the security situation in the Sinai Peninsula is under "full control." He has staked his legitimacy on restoring stability and reviving Egypt's economy.
The suspension of flights would be a further blow to Egypt's troubled tourism industry, which has suffered in the unrest that followed the 2011 Arab Spring popular uprising. The one bright spot for Egypt has been tourism at the Red Sea resorts.
British Transport Secretary Patrick McLoughlin said the British experts would "ensure the right security measures are in place for flights."
"It is when that review is completed that we will allow the flights that are there tonight to depart," he said.
The Irish Aviation Authority followed the British lead and directed Irish airlines to suspend flights to Sharm el-Sheikh Airport and into the airspace of the Sinai Peninsula "until further notice."
The British acted "too soon," said Hany Ramsay, deputy head of Sharm el-Sheikh's airport.
"Other countries might soon follow them, Ramsay told The Associated Press, suggesting there may be political and commercial motives behind the British statement.
"They want to hurt tourism and cause confusion," he added.