The plane that crashed in Egypt’s Sinai Peninsula over the weekend, killing all 224 people on board, could have been subject to external impact but not necessarily a terrorist attack, according to a NYTimes report.

Senior officials at Metrojet, the charter company that operated the aircraft, insist that the plane and crew were not to blame.

“We absolutely exclude the technical failure of the plane, and we absolutely exclude pilot error or a human factor,” said Aleksandr A. Smirnov, the airline’s deputy director for aviation and a former pilot, at a Moscow press conference.

The Airbus A321 was being flown by Russian airline Kogalymavia under the brand name Metrojet and was registered in Ireland in 2012, IrishTimes reported. Air accident investigations are coordinated by the country where the crash occurs and the country where the plane is registered, under international aviation regulations.

The Irish Aviation Authority says it conducted an annual review of the Ireland-registered aircraft’s certifications in April/May and found them satisfactory. The certification attests to an aircraft’s airworthiness.

At least five countries including France, Germany, Russia, Egypt and Ireland have joined the crash investigation.

Mostly Russian vacationers on their way to St. Petersburg from the Egyptian resort of Sharm el Sheikh died in the crash. The plane had reached cruising altitude before falling from the sky, scattering across the Sinai.

Claims by Islamic State are unsubstantiated that it destroyed the aircraft in response to Russia entering the Syrian war, NYTimes reports.

Smirnov said the crash could have been caused by “an external impact on the plane,” but he didn’t say it was a terrorist attack. The investigation will have to determine the cause, he added.

Sharm el Sheikh has been seen as a bright spot in Egypt’s troubled tourism industry, NewYorkTimes reported. Egyptian authorities held it up as a safe haven while a militant insurgency based in Northern Sinai generated concern about travel in other parts of the country.

Following deadly 2005 terror attacks in Sharm el Sheikh and Dahab, the Egyptian government made sweeping technological improvements to Sharm el Sheikh’s security that earned international praise.

Several European countries including Germany, Italy, Ireland, Denmark and Spain lifted travel bans to Egypt in 2014, CairoPost reported.

Egypt had 14.7 million-plus tourists in 2010 but after the 2011 Arab spring, visitors dropped to 9.8 million. In 2012, the number of tourists increased to 11.5 million but fell again in 2013 to 9.5 million.