A United Airlines flight was returning Saturday evening to Newark Liberty International Airport after a problem developed with the left engine during takeoff, officials said. Eyewitnesses reported seeing flames spewing from the engine.

A tire blew during takeoff and flew into an engine, FBI spokeswoman Barbara Woodruff said. The Federal Aviation Administration said it could not confirm that.

The engine was operating properly and the plane was burning fuel before landing, according to the FAA.