LOS ANGELES, Aug. 10 (Xinhua) -- Security was sharply beefed up Thursday at airports in Los Angeles following the discovery of an alleged "mass murder" plot to blow up commercial airliners flying from Britain to the United States.

    In response to the British announcement, the U.S. Department of Homeland Security (DHS) raised the national threat level to its highest rung -- severe, or red -- for commercial flights from the United Kingdom, and to high, or orange, for all flights within the United States.

    British authorities said they foiled the plot and arrested 21 terrorist suspects.

    There was no immediate announcement on which U.S.-bound flights had been targeted for in-flight destruction as part of the plot reported in Britain.

    Five airlines operate 20 daily non-stop flights between London and Los Angeles -- Air New Zealand, American Airlines, British Airways, United Airlines and Virgin Atlantic Airlines.

    Security measures at Los Angeles International Airport are being beefed up even though officials have no information specifically naming the airport as a terror target, said a spokeswoman for Los Angeles World Airports, the agency that operates LAX.

    Passengers are advised to come to LAX between two and three hours early for domestic flights and between three to four hours ahead of time for international flights.

    "Due to the intensified security screening, security screening process is expected to take considerably longer than normal," said spokeswoman Nancy Castles.

    As of 4 a.m. Pacific time, passengers in the United States may no longer carry any liquids -- including drinks, hair gels, and lotions -- onto airplanes, a DHS statement said.

    The ban on liquids reflects the nature of the attack that had been planned in Britain, it said.

    Also banned aboard airliners Thursday are electronic items, including key fobs of the type that switch car alarms on and off.

    "Travelers should also anticipate additional security measures within the airport and at screening checkpoints," the DHS statement said without indicating when the heightened measures would be relaxed.

    Castles said the Los Angeles Airport Police Department was working with the federal Transportation Security Administration and other federal agencies Thursday morning "to implement a range of security measures appropriate to the heightened security." Enditem