CAIRO: 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 on Sunday.

The Airbus A321 crashed 23 minutes after taking off from the Sharm El-Sheikh tourist resort eight days ago, killing all 224 passengers and crew. Daesh 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 on Saturday that the plane appeared to have broken up in mid-air 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.

Asked to explain the remaining 10 percent margin of doubt, the investigator declined to elaborate, but Muqaddam cited other possibilities on Saturday including a fuel explosion, metal fatigue in the plane or lithium batteries overheating.

He said debris was scattered over a 13-km area “which is consistent with an in-flight break-up.”

British Foreign Secretary Philip Hammond said the incident could lead to changes in flight security.

“If this turns out to be a device planted by a Daesh operative or by somebody inspired by Daesh, then clearly we will have to look again at the level of security we expect to see in airports in areas where Daesh is active,” Hammond told the BBC.

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

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