MINNEAPOLIS — Jim Tonjes was high above North America when he bit into a hot turkey sandwich aboard a Delta Air Lines flight and felt a sudden jab in the roof of his mouth.

Glancing down, he noticed what looked like a sewing needle in the food. Another passenger on the plane reported the same thing.

At first, he thought a toothpick meant to hold the sandwich together had punctured the roof of his mouth. When he pulled it out, “it was a straight needle, about 1 inch long, with sharp points on both ends.”

Now US and European authorities are trying to determine how the needles got into meals served on at least four Delta flights from Amsterdam to the United States, and why anyone would place them there.

“We are keeping all options open because at this moment, we have no idea why somebody or something put needles inside the sandwiches,” said Robert van Kapel, a spokesman for Amsterdam’s Schiphol airport.

The FBI and the airport’s police department have opened criminal investigations. The US Transportation Security Administration said it does not view the matter as a threat to national security.

A Delta Air Lines Inc. spokeswoman said the needles were found Sunday in six sandwiches on four flights. Passengers discovered four of them. The flights included one to Minneapolis, one to Seattle, and two to Atlanta.

Tonjes was returning home after a visit to Amsterdam for his mother-in-law’s 90th birthday. The nine-hour flight was about 90 minutes from Minneapolis when flight attendants offered Tonjes, who was seated in business class, a cold Mediterranean salad or the hot turkey sandwich.

Now Tonjes is on a 28-day course of pills (at a cost of $1,400) aimed at warding off any infection, including hepatitis or HIV. His doctors have asked the FBI to tell them right away if they find any residue on the needle.

The sandwiches were made by Gate Gourmet, one of the world’s largest airline caterers, with facilities on five continents. The company serves many airlines, but only Delta flights appeared to be affected. The company said it was investigating.

When the needles were discovered on the first Delta flight, a message went out to other Delta flights, which is why some of the needles were found before they got to passengers.