By Jon Ostrower

CNN

(CNN) -- A Delta Air Lines flight turned back after takeoff from Seattle to Beijing on Thursday night following a "security incident" in the first class cabin.

Initial information indicated an unruly passenger attempted to enter the jet's cockpit, according to two people briefed on the incident.

But Port of Seattle Airport spokesman Perry Cooper said the plane turned back after a passenger attacked a flight attendant in the first class cabin. He said the incident took place in the front part of the twin-aisle aircraft, in the first class cabin.

Several passengers stepped in to subdue the alleged attacker, Cooper said.

Three people were injured in the incident aboard Delta flight 129, including one passenger and one flight attendant, according to Cooper. The unruly passenger was also injured, but he declined medical care.

The flight turned back as it was flying over the western coast of Canada.

Safe return

The Boeing 767 returned safely to Seattle-Tacoma International Airport around 7:40 p.m. local time under a Department of Defense escort, according to the two people briefed on the incident.

A Delta spokeswoman said the flight was not met by a Department of Defense air escort as it returned to Seattle. CNN has reached out to the North American Aerospace Defense Command to get clarification on the discrepancy.

In a statement to CNN, the airline said a passenger was restrained and removed from the flight because of a "security incident" onboard.

Law enforcement officers took the passenger into custody after the flight returned to the gate, Delta said. The flight re-departed for Beijing on Friday shortly after midnight local time.

FBI assisting

The FBI was involved in the response to the incident. But "there is no information to suggest this is a national security threat," said FBI specialist Ayn Dietrich-Williams.

The FBI Seattle field office maintains a regular presence at the airport, and is assisting and interviewing passengers from the flight, according to Dietrich-Williams.

The suspect, a 23-year-old man from Florida, was arrested by the Port of Seattle Police Department, the FBI said in a statement. It said the suspect's initial federal court appearance is Friday.

"The FBI's investigation is ongoing and more details about the incident will be provided and the charges announced at the subject's initial appearance in federal court," the FBI said.

CNN's Keith Allen contributed to this report