Travellers in the U.S. and Europe faced a series of disruptions late Sunday and into the start of the week after a software glitch halted United Airlines traffic and London's Heathrow Airport cancelled more than 100 flights amid intense fog in the British capital.

Heathrow airport said Monday that it had cancelled around 100 of its 1,300 scheduled flights owing to limited visibility at the west London airport.

Late Sunday in the United States, a computer error led to a so-called "ground halt" for United Airlines, resulting in the cancellation of domestic flights for United Continental Holdings Inc (UAL) - Get Report subsidiary for over an hour. The ground stop was lifted by around 02:00 GMT, although the company's last communication on the disruption, a Tweet sent at around 03:00 GMT, cautioned that "additional delays" are expected.

United Continental is the third-largest carrier in the U.S., operating more than 4,500 flights a day, with a fleet of more than 720 mainline aircraft. American Airlines, the country's largest, offers an average of 6,700 flights each day on its nearly 950 aircraft. Delta Air Lines has 830 aircraft.

Continental shares closed at $75.24 each Friday in New York, up 1.65% on the session, extending their three-month gain to more than 35.2%.