Russia is suspending all flights to Egypt following indications that last week's plane crash which killed all 224 people on board was caused by a bomb.
President Vladimir Putin has also asked for up to 50,000 Russian holiday-makers currently in Egypt to be brought home.
Intercepted militant "chatter" suggests a bomb was put in the hold before take-off. French aviation officials told the BBC there was no technical failure.
The Metrojet Airbus A321 was flying from Sharm el-Sheikh to St Petersburg when it came down in Sinai on Saturday. Most of the victims were Russian.
Analysis: Sally Nabil, BBC News, Sharm el-Sheikh
The Russian decision to suspend flights to Egypt is a major blow to tourism, which is a lifeline to the Egyptian economy. More than 30% of the tourists who visit Egypt each year come from Russia.
Now the picture has become increasingly grim. Shopkeepers and hotel owners are pretty worried. "I don't know what tomorrow is going to bring us. We are already suffering," a shopkeeper tells me.
The tourism industry has been struggling since the revolution in 2011, due to political uncertainty. In recent months, there was a relative sense of stability so things took a better turn.
But after the latest developments, it's hard to tell when tourism will recover. The timing of the plane crash couldn't be worse - autumn and winter are supposed to be the peak of the tourist season in Egypt. Known for its warm weather, bright sunshine and lovely beaches, the country was getting ready for some busy weeks. But the beautiful landscape won't be enough at the moment to attract tourists.
Militants from the Sinai Province group, linked to Islamic State, say they downed the plane, but not how. IS has called for a war against both Russia and the US over their air strikes in Syria.
The BBC understands that UK officials received intelligence based on intercepted communications between militants in the Sinai Peninsula, indicating an explosive device may have been put inside or on top of the luggage just before the plane took off.
French air accident investigators cited by AFP news agency said the flight data recorder had shown that "everything was normal during the flight, absolutely normal, and suddenly there was nothing", suggesting a "violent, sudden" explosion. A similar conclusion was drawn by another investigator speaking to France 2 television.
Senior French aviation officials familiar with the investigation told the BBC's Chris Bockman in Toulouse that they had ruled out the possibility that there was any fault or technical issue with the plane that led to the crash.
Experts in Moscow are investigating pieces of debris from the crash site, Russian officials say.
After announcing the suspension of the Russian flights to Egypt, President Putin had a telephone conversation with Egyptian President Abdul Fattah al-Sisi.
They agreed to continue "active co-operation" on flight safety, a statement from the Kremlin said.
The UK estimates that 19,000 of its nationals remain stranded in Sharm el-Sheikh.
Since Wednesday, several countries have joined Britain in restricting travel to Sharm el-Sheikh. They include Belgium, the Netherlands and Germany.
The US has announced it is stepping up security screening of items on US-bound flights from some airports in the Middle East. The Homeland Security statement did not name which airports it was targeting.
Tourism contributed more than 12% to Egypt's economy in 2013 and the latest measures will hit it hard, analysts say. One in five foreign tourists in Egypt is Russian.
Sinai Province militants
- Most active insurgent group in Egypt, with 1,000-1,500 members
- Operating in Sinai Peninsula since 2011
- Pledged allegiance to Islamic State group in November 2014
- Carries out suicide bombings, shootings, beheadings; dozens of Egyptian soldiers killed.
Are you in Sharm el-Sheikh? Are you flying back to the UK? If you have any information to share with the BBC, you can email firstname.lastname@example.org.
Please include a contact number if you are willing to speak to a BBC journalist. You can also contact us in the following ways: