Air India flight 191, traveling from Mumbai to Newark, New Jersey, landed safely after being diverted at 10:15 a.m. BST (0915 GMT). The Boeing 777 was parked on an isolated stand far from the airport's normal operations.
All 327 passengers were taken off the plane and were "served snacks and other beverages," said Dhananjay Kumar, a spokesman for Air India.
The U.K.'s Ministry of Defense did not identify the plane but did say that Typhoon aircraft safely escorted a civilian aircraft to the airport, which lies around 37 miles (60 kilometers) northeast of the center of London.
British media reported earlier Thursday that there was a bomb threat onboard but officials did not comment on the nature of the security alert.
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