Russian Plane Crash, Nov. 8, 2015
Orthodox believers light candles for the victims of the Russian Metrojet Airbus A321 crash in Egypt last weekend during a service at St. Isaac's Cathedral in St. Petersburg. Russia, Nov. 8, 2015. Olga Maltseva//AFP/Getty Images

CAIRO (Reuters) — Investigators of the Russian plane crash in Egypt are "90 percent sure" the noise heard in the final second of a cockpit recording was an explosion caused by a bomb, a member of the investigation team told Reuters Sunday. The Airbus A321 crashed 23 minutes after taking off from the Sharm al-Sheikh tourist resort eight days ago, killing all 224 passengers and crew members. Islamic State group militants fighting Egyptian security forces in Sinai said they brought it down.

"The indications and analysis so far of the sound on the black box indicate it was a bomb," said the Egyptian investigation team member, who asked not to be named due to sensitivities. "We are 90 percent sure it was a bomb." His comments reflect a higher degree of certainty about the cause of the crash than the investigation committee has so far declared in public.

Lead investigator Ayman al-Muqaddam announced Saturday that the plane appeared to have broken up in midair while it was being flown on auto-pilot, and that a noise had been heard in the last second of the cockpit recording. But he said it was too soon to draw conclusions about why the plane crashed.

Confirmation that militants brought down the airliner could have a devastating impact on Egypt's lucrative tourist industry, which has suffered from years of political turmoil and was hit last week when Russia, Turkey and several European countries suspended flights to Sharm al-Sheikh and other destinations.

It could also mark a new strategy by the hardline Islamic State group, formerly known as either ISIL or ISIS, which holds large parts of Syria and Iraq.

Asked to explain the remaining 10 percent margin of doubt, the investigator declined to elaborate, but Muqaddam cited other possibilities Saturday, including a fuel explosion, metal fatigue in the plane or lithium batteries overheating. He said debris was scattered over an 8-mile area, "which is consistent with an in-flight breakup."

'Game Changer'

"What happened in Sharm al-Sheikh last week, and to a lesser extent with the ... [Germanwings] aircraft, are game changers for our industry," Emirates Airlines President Tim Clark said, referring to the crash of a Germanwings airliner in the French Alps in March, which is believed to have been crashed deliberately by its co-pilot. "They have to be addressed at industry level because no doubt the countries -- U.S., Europe -- I would think will make some fairly stringent, draconian demands on the way aviation works with security," he said at the Dubai Airshow.

Clark said he had ordered a security review but was not suspending any flights as a result of the disaster. Emirates does not operate regular flights to Sharm al-Sheikh.

British Foreign Secretary Philip Hammond also said the incident could lead to changes in flight security. "If this turns out to be a device planted by an ISIL operative or by somebody inspired by ISIL, then clearly we will have to look again at the level of security we expect to see in airports in areas where ISIL is active," Hammond told the BBC.

The Islamic State group wants to establish a caliphate in the Middle East.

Islamic State militants fighting security forces in Egypt's Sinai Peninsula have said they brought down the aircraft as revenge for Russian airstrikes against Islamist fighters in Syria. They said they would eventually tell the world how they carried out the attack.

If the group was responsible, it would have carried out one of the highest-profile killings since al Qaeda flew passenger planes into New York's World Trade Center in September 2001.

Russia has returned 11,000 of its tourists from Egypt in the last 24 hours, the RIA news agency said Sunday, a fraction of the 80,000 Russians who were stranded by the Kremlin's decision Friday to halt all flights to Egypt.

In St. Petersburg, where the flight was headed Oct. 31, the bell of St Isaac's Cathedral rang 224 times and a service was held in memory of the victims.

Russia has sent specialists to conduct a safety audit of Egypt's airports and to provide recommendations on additional measures, Arkady Dvorkovich, deputy prime minister, was quoted as saying by Russian agencies. Dvorkovich, the head of a government group created Friday to deal with suspended flights to Egypt, added that a second group was going to Egypt Sunday and a third would be sent later.

A British official said Saturday it could take 10 days for all British tourists to be flown home.

(Reporting by Ahmed Mohamed Hassan and Michael Georgy; Additional reporting by Nadia Saleem in Dubai, William James in London, Denis Pinchuk in Moscow and Mikhail Antonov in St. Petersburg; Writing by Michael Georgy and Dominic Evans; Editing by Janet Lawrence)