Britain has said it is concerned that a Russian airliner that crashed in Sinai may have been brought down by a bomb, prompting it to temporarily suspend flights from Egypt's Red Sea resort of Sharm el-Sheikh.
Wednesday's announcement came four days after the Russian Airbus crashed in northern Sinai, killing all 224 people on board, just 23 minutes after taking off from Sharm el-Sheikh.
"While the investigation is still ongoing we cannot say categorically why the Russian jet crashed, the office of Prime Minister David Cameron said in a statement.
"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," he said.
A Russian aviation source told the Reuters news agency that the investigation into the crash is looking into the possibility of an object stowed on board causing the disaster.
"There are two versions now under consideration: something stowed inside [the plane] and a technical fault," the source said.
"But the airplane could not just break apart in the air - there should be some action. A rocket is unlikely as there are no signs of that."
Fighters from the Islamic State of Iraq and the Levant (ISIL) have said they were responsible for downing the plane, but have provided no details, prompting scepticism about the veracity of the claim.
British aviation experts have been dispatched to Sharm el-Sheikh to assess the security situation and flights back to the UK from the resort are being held until the assessment is completed as expected later on Wednesday, the statement said.
"We recognise that this information may cause concern for those in Sharm and indeed for those planning to travel to Sharm in the coming days," Downing Street said.
"We have deployed extra consular staff to Sharm who will be on hand at the airport, working with the airlines, to assist British holidaymakers there."
Cameron will also hold an emergency cabinet meeting on the issue on Wednesday.
"We would underline that this is a precautionary step and we are working closely with the airlines on this approach," the statement said.