UK investigators looking at what caused a Russian airliner to crash in Egypt believe a bomb was put in the hold prior to take-off.
The British government suspended all flights to and from the Egyptian resort of Sharm el-Sheikh two days ago.
It had received intelligence based on intercepted communications between militants in the Sinai Peninsula.
However, both Egypt and Russia have said it is too early to draw conclusions.
The Metrojet Airbus A321 was flying from Sharm el-Sheikh to St Petersburg when it came down in Sinai on Saturday, killing all 224 people on board. Most of the victims were Russian.
Britons stranded in Sharm el-Sheikh are due to begin returning on Friday, but will only be allowed to bring hand luggage.
One of the main airlines operating from the resort, Easyjet, says its plans to return passengers to Europe on Friday have been sharply curtailed by the Egyptian authorities, with only two of its 10 flights leaving.
French-Dutch airline KLM is also restricting passengers flying from Cairo to hand luggage only.
Anger in Moscow and Cairo: Jonathan Marcus, BBC diplomatic correspondent
The speed with which the British government pointed to terrorism as the possible cause of the downing of the Russian Airbus over the Sinai Peninsula has not gone down well in either Cairo or Moscow.
For the Egyptians the stakes are obvious: Sharm el-Sheikh and the wider tourism industry are crucial elements of its economy. This episode has punctured the long-held Egyptian narrative that Sharm el-Sheikh is insulated from the wider chaos in the Sinai.
For the Russians, an attack linked to so-called IS is also problematic. IS is the declared target of its air operations in Syria, but in reality Russian warplanes have largely been striking other rebel groups.
IS may now find itself in Russia’s sights. But if IS did bring down the airliner, this could exacerbate concerns amongst Russian public opinion that their country’s engagement in Syria is provoking some unpleasant blow-back.
BBC security correspondent Frank Gardner says that although British officials have not ruled out the crash was caused by a technical fault, they think that is increasingly unlikely.
New intelligence was received on Wednesday. The UK government’s Joint Terrorism Analysis Centre (JTAC) has spent the past few days assessing what brought the plane down.
Security service investigators suspect someone with access to the aircraft’s baggage compartment inserted an explosive device inside or on top of the luggage just before the plane took off, our correspondent adds.
Sinai-based militants linked to the Islamic State (IS) group said they destroyed the plane, but did not say how. IS has called for a war against both Russia and the US over their air strikes in Syria.
US President Barack Obama told a CBS radio station on Thursday that he thought there was “a possibility” that there was a bomb on the downed jet.
“We’re taking that very seriously,” he said.
Since Wednesday, several countries have joined Britain in restricting travel to Sharm el-Sheikh.
France and Belgium are advising their citizens against all but essential travel there. The Netherlands is warning against travelling via Sharm el-Sheikh airport.
German airline Lufthansa says its subsidiaries Edelweiss and Eurowings are halting flights to Sharm el-Sheikh (from Zurich and Duesseldorf respectively) as a “precautionary” measure, and return flights for customers already there will be arranged.
Russian planes are still flying to and from the resort.
Dmitry Peskov, spokesman for President Vladimir Putin, said only the official investigation could determine what happened, while Egypt called Britain’s decision to suspend flights unjustified.
Egypt’s President Abdul Fattah al-Sisi, who has been on a visit to the UK, told reporters that security at the airport was tightened 10 months ago at the UK’s request.
However, he said he understood Britain’s concern.
Egypt is leading the investigation into the air disaster, with the help of Russian and other foreign experts.
