Russia has suspended all flights to Egypt following indications that the crash near Sharm el-Sheikh was caused by a bomb.
President Vladimir Putin made the announcement after UK investigators said they believed a bomb was put in the plane’s hold prior to take-off, killing all 224 people on board.
Militants linked to ISIS say they downed the plane.
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.
Militants from the Sinai Province group, linked to ISIS, have not said how they destroyed the plane. ISIS has called for a war against both Russia and the US over their air strikes in Syria.
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.
Experts in Moscow are investigating pieces of debris from the crash site, Russian officials say.
Russia is also working to repatriate as many as 45,000 Russian holidaymakers currently in Egypt – and an official said it could take up to a month to bring them home.
Since November 4, several countries have joined Britain in restricting travel to Sharm el-Sheikh. They include Belgium, the Netherlands and Germany.
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.
According to Egypt’s PM Sharif Ismail, a technical fault was the most likely to cause Russia’s Kogalymavia plane crash in Sinai dismissing claims from Islamic State militants that they were responsible.
An investigation is under way after all 224 people on board were killed.
However, three airlines – Emirates, Air France and Lufthansa – have decided not to fly over the Sinai Peninsula until more information is available.
The plane’s black boxes have been found and sent for analysis, officials said.
The Kogalymavia Airbus A-321 came down early on October 31, shortly after leaving the resort of Sharm el-Sheikh for the Russian city of St Petersburg.
Egypt’s civil aviation minister Hossam Kamal said there had been no sign of any problems on board the flight, contradicting earlier reports that the pilot had asked to make an emergency landing.
An Egyptian official had previously said that before the plane lost contact with air traffic controllers, the pilot had said the aircraft was experiencing technical problems and he intended to try to land at the nearest airport.
Russian and French investigators have joined the Egyptian-led probe, along with experts from Airbus, which is headquartered in France.
A criminal case had been opened against Kogalymavia for “violation of rules of flight and preparation for them”, Russia’s Ria news agency reported.
Police have searched the company’s offices.
Kogalymavia spokeswoman Oksana Golovina insisted the 18-year-old plane was “fully, 100% airworthy” and added that the pilot had 12,000 hours of flying experience.
In Sinai itself, where jihadists groups are active, militants allied to IS made a claim on social media that they brought down flight KGL9268.
However, Egyptian PM Sharif Ismail dismissed the claim, saying experts had confirmed that a plane could not be downed at the altitude the Airbus 321 was flying at.
Russian Transport Minister Maksim Sokolov told Interfax news agency that “such reports cannot be considered true”. No evidence had been seen that indicated the plane was targeted, he said.
Egypt’s civilian aviation ministry said the plane had been at an altitude of 31,000ft when it disappeared.
Security experts say a plane flying at that altitude would be beyond the range of a shoulder-launched surface-to-air missile (Manpad), which Sinai militants are known to possess.
However, German carrier Lufthansa said it would avoid flying over the Sinai peninsula “as long as the cause for today’s crash has not been clarified”.
On Saturday evening, Air France-KLM and Emirates said they were following suit.
British Airways and easyJet said their routes were regularly reviewed, but that they had no plans to alter their routes to and from Sharm el-Sheikh.
Two American women tourists have been kidnapped by gunmen in Egypt’s Sinai peninsula, according to security sources.
The American tourists were travelling in a small bus with three other tourists from St. Catherine’s monastery on Mount Sinai to the Red Sea resort of Sharm el-Sheikh when it was stopped by the gunmen.
One official told the Reuters news agency that the men wanted a ransom.
Bedouins kidnapped 25 Chinese workers in northern Sinai earlier this week, but released them unharmed after a day.
They were demanding the release of fellow tribesman who was jailed after the 2004 bomb attack at the resort of Taba that killed 31 people.
The Americans were reportedly travelling through the Wadi al-Sual area of Sinai, about 40 km (25 miles) from St. Catherine’s, when a vehicle carrying masked men armed with machine-guns forced the bus to stop.
The gunmen took the tourists’ money and valuables before grabbing the two women, forcing them into a vehicle and fleeing into the mountains.
Their Egyptian tour guide was also kidnapped, AFP news agency said.
The three other tourists who had been in the bus were left behind.
Police teams assisted by a military plane are searching for the Americans, state television reported.
One officer believed the kidnappings were meant to pressure the authorities to release Bedouins detained for their role in kidnapping the Chinese workers; others said the motive was financial.
Tribesmen in Sinai have been involved in a series of confrontations with security forces in recent months.
A gas pipeline from Egypt to Israel has also repeatedly been sabotaged, though Sinai’s tourist resorts have remained largely secure.