By Sandra Endo

Washington (CNN) - It's not what you want to find when you bite into a sandwich: a needle.

But that's exactly what happened aboard four Delta flights.

Now several investigations are underway to find out just where the needles came from and how the airline and the sandwich provider can prevent a similar incident from happening again.

The FBI and local authorities in the Netherlands are trying to find out how the needles got into those turkey sandwiches.

A Delta spokesperson says the needles were found in sandwiches on flights from Amsterdam to Minneapolis, Seattle, and two flights to Atlanta.

Two of the needles were found by passengers, and one was discovered by an air marshal.

When Delta found out about the needles in the food, the airline says it notified all 18 flights from Amsterdam to stop serving the sandwiches.

"I bit down not on the sharp side but on the flat side. It could have been a bad injury orally but had I taken a big swallow and swallowed that I'd have a needle inside and that would be very concerning to me," said passenger Dr. Jack Drogt.

Gate Gourmet provided the sandwiches, which were prepared in Amsterdam, to Delta.

In a statement, a spokesperson for the company says, "This is a terribly upsetting situation. First and foremost is the safety of the traveling public. There's nothing more important to us at all than the safety of the passengers and crews."

Gate Gourmet says it's fully cooperating with the FBI and local authorities in the Netherlands, and is conducting its own full scale investigation.

The company says it does provide food to other airlines, but has received no other reports or complaints.

CNN