LONDON — BRITISH security authorities ordered a red alert in London and other main cities yesterday after terrorists, thought to be members of the outlawed Irish Republican Army, launched a mortar attack on 10 Downing Street. Government officials later spoke of their fears that the IRA had taken a decisive step to intensify its campaign of terror in mainland Britain. They compared the missile attack to the IRA bombing in 1984 of a hotel in Brighton, England, during a meeting of the Conservative Party. In that attack, Margaret Thatcher, the then-prime minister, narrowly escaped being killed.
Yesterday's mid-morning attack on the home and office of Prime Minister John Major was made as Mr. Major chaired a meeting of the Gulf war cabinet.
The missiles were launched from a nearby parked van, which had been driven up Whitehall, the main thoroughfare, and parked outside the Ministry of Defense. Bystanders said two people opened the rear doors and fired three rockets toward the entrance of Downing Street 200 yards way. There was one huge explosion and two smaller ones.
One shell landed in the back garden of 10 Downing Street, a Scotland Yard officer said. It shattered the windows of the room in which the war cabinet was meeting. The other two landed at the rear of the Foreign Office. Two people were slightly injured.
Major and Home Secretary Kenneth Baker ordered a thorough review of security in and around Whitehall.
Scotland Yard officials said mortar bombs and crude rockets have been used many times in Northern Ireland. If the IRA was responsible for yesterday's incident, it would be the first such missile attack on the mainland.