Intruder triggers Heathrow security alert

LONDON, England (CNN) -- A man was arrested on the runway at London's Heathrow Airport on Wednesday, setting off a major security alert on the eve of a visit by Queen Elizabeth to open a landmark terminal building.

Witnesses said the intruder scaled a perimeter fence and sprinted onto the runway with a backpack before being tackled by armed police officers, according to the UK's Press Association.

Police carried out a controlled explosion on the bag, but no explosives were found, the Metropolitan Police said.

"Airport police swiftly apprehended a man near the northern runway of Heathrow this afternoon. The police arrested the man about 2 p.m. within the airport perimeter," the British Airport Authority said in a statement.

The incident was the second serious security lapse at Heathrow in recent weeks. Greenpeace activists were able to climb on top of a passenger jet last month in protest of plans for a third runway at the airport.

It also occurred one day before the official opening of the airport's Terminal 5 building by Queen Elizabeth.

The runway remained partially closed after the alert, BAA said. A spokesman for British Airways told PA that flights were being delayed and that "a small number" of cancellations were expected.

Heathrow, one of the world's busiest airports, has been targeted in recent months by environmental campaigners opposed to airport expansion in the UK. Both Greenpeace and campaigning group Plane Stupid have denied involvement in the incident, PA reported. E-mail to a friend

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