The chief investigator in the EgyptAir plane crash that killed all 66 people on board last week says search teams in the Mediterranean have picked up a beacon believed to be from the doomed aircraft.

Ayman al-Moqadem says this narrows down the search to a 5 kilometer (3 mile) radius. He insisted that this doesn't mean the flight data and cockpit voice recorders - the so-called "black boxes" - have been found.

Al-Moqadem says finding the boxes requires highly sophisticated technology. He says the signal that was picked up comes from one of the devices on the plane transmitting its location. He spoke to reporters on Thursday.

France's air accident investigation agency has said a French naval ship specialized in underwater searches will help search for the black boxes.

Sign up for the Newsletter

Get the best of delivered to your inbox every day.

(© 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed)