Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Three air marshals were among the 66 people aboard EgyptAir Flight MS804 that crashed while flying over the Mediterranean Sea early Thursday, authorities said.

France's transport chief Alain Vidalies told reporters that having that many security officers on such a flight was “the usual practice." He added that the plane — which can carry up to 189 passengers — was not transporting any freight.

Related: Missing EgyptAir Jet Raises Fears of 'Worst-Case Scenario'

Former NTSB investigator Greg Feith told MSNBC that Egypt had boosted security recently, which could explain the number of officers on board.

"The only other reason to have security personnel like we do here in the U.S. is if they were transporting some sort of prisoner or someone of interest," Feith added. "But most likely this was similar to our federal air marshals flying on this flight.”

Egyptian aviation security has been under intense scrutiny since a Russian Metrojet passenger plane crashed after taking off from Sharm el-Sheikh airport on Oct. 31, killing all 224 people on board.