Britain said on Thursday there was a significant possibility that Islamic State's Egyptian affiliate was behind a suspected bomb attack on a Russian airliner that killed 224 people in the Sinai Peninsula.
Asked if he thought Islamic State militants were responsible for the disaster, Foreign Secretary Philip Hammond said: "ISIL-Sinai have claimed responsibility for bringing down the Russian aircraft, they did that straight away after the crash.
"We've looked at the whole information picture, including that claim, but of course lots of other bits of information as well, and concluded that there is a significant possibility," he said on Sky television.
U.S. and European security sources say evidence now suggests that a bomb planted by Islamic State's Egypt affiliate - Sinai Province - was the likely cause of the crash. The sources stressed they had reached no final conclusions about the crash.
Islamic State, which wants to create a caliphate across the Muslim world, is also called ISIS and ISIL. Russia, an ally of Syrian President Bashar al-Assad, launched air raids against opposition groups in Syria including Islamic State on Sept. 30.
The hardline group has called for war against both Russia and the United States in response to their air strikes in Syria.
Britain has decided to stop flights from Egypt's Sharm El Sheikh resort to gain more time to assess security in the town, where the Russian plane started its ill-fated journey.
Islamic State, which also has a presence in Egypt's neighbor Libya, is waging a bloody campaign of suicide bombings and shootings in Egypt designed to topple the government of President Abdel Fattah al-Sisi.
The Egyptian leader is currently on a state visit to Britain, which like other Western powers sees Cairo as critical to efforts to counter militancy.
A senior Russian lawmaker said Britain's decision to stop flights from Egypt's Sharm El Sheikh resort, where the flight originated, was motivated by London's opposition to Russia's actions in Syria, the RIA Novosti news agency reported.
"There is geopolitical opposition to the actions of Russia in Syria," said Konstantin Kosachev, a senior member of Russia's upper house of parliament, when asked about Britain's decision.
If a bomb killed the 224 passengers and crew aboard the Airbus A321, that would almost certainly undermine Egypt's tourism industry, which is still recovering from years of political turmoil.
A Russian aviation official said the investigation was looking into the possibility of an object stowed on board causing the disaster.
Islamic State, which controls swathes of Iraq and Syria and is battling the Egyptian army in the Sinai Peninsula, said again on Wednesday that it brought down the airplane, adding it would eventually tell the world how it carried out the attack.
Egypt, a close ally of the United States and the most populous Arab country, dismissed a similar claim of responsibility for the crash by Islamic State on Saturday.
Caution among Egypt officials in assessing the cause of the crash has not eased anxiety among tourism companies that handle visitors to Egypt's ancient sites and Red Sea resorts.
Shares on Thomas Cook opened down 2.1 percent as the United Kingdom canceled flights to Egypt, which depends heavily on tourism to generate hard currency.
Sisi has described Islamist militancy as an existential threat to the Arab world and the West and has repeatedly called for greater international efforts to combat the militants.
People mourn as they arrive at Dvortsovaya Square to commemorate victims of the air crash in Egypt in St. Petersburg, Russia, November 3, 2015. Photo: Reuters/Peter Kovalev
Britain said it was working with airlines and Egyptian authorities to put in place additional security and screening measures to allow Britons in Sharm el-Sheikh to get home, but that would take time and there would be no flights returning from the resort on Thursday.
Late on Wednesday, the Irish Aviation Authority (IAA) directed all Irish airlines on Wednesday not to fly to or from the Sinai Peninsula until further notice. The Russian-operated plane was registered in Ireland and the IAA is taking part in the official investigation into the crash.
Security experts and investigators have said the plane is unlikely to have been struck from the outside and Sinai-based militants are not believed to possess the technology to shoot down a jet from a cruising altitude above 30,000 feet.
Sinai Province has killed hundreds of Egyptian soldiers and police since Sisi, as army chief, toppled Islamist President Mohamed Mursi in 2013 after mass protests against his rule.
Sisi was elected president last year on promises he would stabilize Egypt and rebuild its shattered economy. Critics say his tough crackdown on Islamists will only create more radicals in Egypt, which has fought militants for decades.