New York (CNN) -- A Berlin-bound United Airlines flight returned Saturday night to Newark Liberty International Airport after a problem developed in the left engine, officials said.

Eyewitnesses reported seeing flames spewing from engine right after the plane took off.

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.

Flight 96, with 173 passengers and crew, circled the airport and burned fuel before landing at 8:05 p.m., according to the FAA. United described it as a "mechanical issue."

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The crew of the Boeing 757 reported a problem after it left New Jersey for Berlin, said FAA spokeswoman Kathleen Bergen. The engine was operating properly before it landed, she told CNN.

Eyewitness Keisha Thomas, who was traveling on the New Jersey Turnpike, said she witnessed fireballs near a wing shortly after the plane took off.

Thomas heard a loud sound, describing it as "pow, pow, pow."

Djenaba Johnson-Jones, who lives across the river from the airport, said she heard an unusual noise and saw fire, but not smoke, coming from the aircraft's left engine.

Eyewitness Dennis Ostolaza said he heard a "propeller sound" akin to a military helicopter as the plane gained altitude after takeoff, with "black smoke and fire spitting out of the engine."

The flight left the gate at 5:53 p.m.; witnesses reported seeing the engine flames shortly before 6:30 p.m.

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Based on the article and the following list of answers, write a list of questions.

1. Barbara Woodruff
2. Flight 96
3. 173
4. 8:05 p.m.
5. Newark Liberty International Airport
6. Berlin
7. No
8. Boeing 757
9. An eyewitness
10. On the New Jersey Turnpike
11. Yes
12. "pow, pow, pow."
13. 5:53 p.m
14. right after the plane took off.
15. a "mechanical issue."
16. flames
17. unknown
18. Djenaba Johnson-Jones
19. No
1. Who is an FBI spokeswoman?
2. On what flight did this occur?
3. How many people on board?
4. What time did it touch down on the ground?
5. Where did it land?
6. Where was it supposed to be going to?
7. Did problems occur in the right engine?
8. What kind of plane was it?
9. Who is Keisha Thomas?
10. Where was she?
11. Did she hear anything?
12. How did she say it sounded?
13. When did the flight leave the airport
14. When did the flames occur?
15. What did United say was the cause?
16. What was coming out of the engine?
17. What caused this all?
18. Who lives across the river?
19. Did she see smoke?