The cockpit recorder on the Russian passenger plane that crashed in Egypt last Saturday logged an unspecified noise in the final second before it ceased operation, the head of the Egyptian committee tasked with investigating the incident said Saturday. Authorities say they have yet to reach a conclusion about the cause of the crash, which killed all 224 people aboard the Airbus A321.

Egyptian officials are still exploring possible causes, said Ayman al-Muqaddam, the head of the Egyptian investigatory panel. The officials reportedly suspect an explosion caused the crash, but have yet to determine whether terrorists targeted the plane, a source familiar with the investigation told Reuters.

Authorities in the U.K. and U.S. have said intelligence information indicated a bomb downed the Russian plane. However, Egypt has stopped short of attributing the plane crash to terrorism. But a top Egyptian official criticized other countries for lackluster efforts to combat terrorism in the Middle East.

“The spread of terrorism, which we have for a long time called on our partners to tackle more seriously, did not get through to many of the parties which are now exposed and which are currently working for the interests of their citizens to face this danger,” Reuters quoted Egyptian Foreign Minister Sameh Shoukry as saying at a press conference.

Russia suspended all passenger-plane flights to Egypt Friday because of the crash, although the Kremlin has been adamant that this action wasn’t an indication the Russian government suspected a terrorist attack, the Guardian reported. The suspension of commercial flights stranded almost 80,000 Russian citizens vacationing in Egypt. Russia sent 44 planes to retrieve its stranded nationals from Egyptian resorts Saturday, Agence France-Presse said.

U.K. and U.S. agents intercepted communications among militants that suggested a branch of the Islamic State group may have placed a bomb on the Russian plane, the Associated Press reported. But neither country has reached a final conclusion about the cause of the incident.