While flying overnight from Paris to Cairo, an EgyptAir Airbus A320 disappeared from radar over the eastern Mediterranean Sea Thursday. Flight MS804 was carrying 56 passengers and crew on board, BBC reported.

According to a list from EgyptAir, the 56 passengers included 30 Egyptians, 15 French nationals, one Briton, one Kuwaiti, one Saudi, one Chadian, one Portuguese from Algeria, one Canadian, and one Sudanese.

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The plane left from Paris’ Charles de Gaulle Airport at 11:09 p.m. local time Wednesday and was scheduled to arrive in Cairo approximately four hours later at 3:15 a.m. Thursday local time.

The plane checked in with Greek traffic controllers at 1:24 a.m. and 1:48 a.m. local time. Greek authorities say the pilot was “cheerful,” CNN reported.

Greek controllers tried to contact the plane again around 2:27 a.m. Thursday, but received no response despite repeated calls. Once the plane was in Cairo airspace, around 2:29 a.m., it swerved sharply then rapidly dropped from 37,000 feet south-southeast of Kumbi, an aviation reporting point in the Mediterranean Sea, CNN reported.

French President Francois Hollande announced in a televised address that flight MS804 had “crashed” and was “lost,” BBC reported.

Both Egypt and Greece deployed ships and aircraft for search and rescue operations at 2:45 a.m. local time. The U.S. military is on standby to help.

The cause behind this disappearance is more likely to be terrorism than a mechanical issue, Egypt’s civil aviation minister said, according to CNN.

UPDATE: “EGYPTAIR denies all misleading information published by news websites and on the social media channels regarding the reasons of the disappearance of EGYPTAIR flight MS804 and the company confirms that the reason of [the] disappearance hasn’t been yet confirmed,” the airline said in a statement.