The crash of the Russian airliner in Egypt was "more likely than not" caused by an explosive device smuggled on to the plane by "operatives" either inspired or related to the Islamic State extremist group, British Foreign Secretary Philip Hammond said Monday.

Hammond told reporters at U.N. headquarters in New York on Monday that Britain has shared some information with its partners but cannot share some "sensitive intelligence."

Nonetheless, he expressed hope that countries would "draw conclusions" from Britain's decision to be first to suspend flights to Sharm el-Sheikh, a major tourist destination.

The claim comes one day after a member of the Egyptian team investigating the crash said he and his colleagues are "90 percent sure" the plane was brought down by a bomb. 

Reuters, which reported the unnamed team member's comments, said he had asked not to be named due to "sensitivities."

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"The indications and analysis so far of the sound on the black box indicate it was a bomb," the investigator added. His comments are the first reported acknowledgement from anyone connected with the investigation that the Airbus A321-200 was the target of an attack.

Also Monday, Israel's defense minister said there was a "high probability" that the Russian airliner was brought down by a bomb. Moshe Yaalon told reporters he "would be surprised" if a planted explosive device did not cause the crash.

"There is a high probability that this was a terror attack by an explosive device," he said.

Yaalon noted that Israel is not involved in the investigation. He said his opinion was based on "what we hear and understand."

Israel borders Egypt's Sinai desert, the site of the crash. It maintains tight security ties with Egypt and keeps a close eye on Islamic militant groups operating in the desert peninsula.

A team from the International Civil Aviation Organization began inspecting Cairo's international airport Monday. The checks are expected to include security and baggage handling.

Monday's visit was scheduled before the Oct. 31 crash in the Sinai Peninsula that killed all 224 people onboard the Russian Metrojet Airbus A321.

The inspection is to end on Thursday. The ICAO is a U.N. specialized agency that aims to support a safe and secure civil aviation sector.

Metrojet Flight 9268 crashed 23 minutes after taking off from Sharm el-Sheikh.

Meanwhile, the first of three teams of Russian inspectors was dispatched to the country to examine airport security. Russian Deputy Prime Minister Arkady Dvorkovich did not give details on what specific security issues the inspections teams would be examining. Dvorkovich said that 11,000 Russians were flown home from Egypt on Saturday and an even larger number were expected to leave Sunday, according to Russian news agencies.

Security officials at the Sharm el-Sheikh airport have told The Associated Press that the facility has long had gaps in security, including a key baggage scanning device that often is not functioning and lax searches at an entry gate for food and fuel for the planes. One security official said drugs and weapons slip through security checks at the airport because poorly paid policemen monitoring X-ray machines can be bribed.

A spokesman for Egypt's Aviation Ministry, Mohamed Rahma, dismissed the accounts of inadequate security, saying "Sharm el-Sheikh is one of the safest airports in the world," without elaborating.

Egyptian authorities have bristled at the allegations of lax security, with some blaming an anti-Egypt bias in the foreign media. Those sensitivities were on display Sunday as foreign camera crews were prevented from filming inside the Sharm el-Sheikh airport, along the city's main tourist strip in Naama Bay, or in other public spaces.

In Russia, more than a thousand mourners packed into the landmark St. Isaac's Cathedral in St. Petersburg for a memorial service for the victims. Attendees lit candles and stood in silence as the cathedral bells rang 224 times to remember each victim.

"We came to the service today with all our family to support the people in our common grief," said Galina Stepanova, 58.

Stepanova said she believed the plane was downed by a bomb, but said that Russia should continue its airstrike campaign against the Islamic State group and other insurgents in Syria.

"We have a rightful cause to help Syria in its fight against terrorism," she said.

Mikhail Vishnyakov, a 42-year-old sales manager who attended the service with his family, said he did not want to rush to conclusions about the cause of the plane crash until the investigation was complete.

"If it was a terrorist act, I don't think it was directed exactly against Russia. It could well be directed against any other plane of any other country. It was for a good reason that other countries began to take their tourists from Egypt," Vishnyakov said.

The Associated Press contributed to this report.

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