A United Airlines Boeing 737 returned to LaGuardia Airport minutes after takeoff Wednesday morning -- after the crew of another plane saw fluid leaking from the left engine.

Flight 1496 landed without incident and there were no reported injuries. It was not immediately clear how many passengers were on board.

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The Federal Aviation Administration said the Chicago-bound flight took off from Runway 13 at 7:37 a.m. and said the crew of "another aircraft" noticed fluid leaking from the left engine -- and reported it to authorities.

The United flight then elected to return to LaGuardia as a precautionary measure, the FAA said. The flight landed safely on Runway 22.

The source of the fluid leak is under investigation.