The new leader of Oxfordshire County Council, Keith Mitchell, sent a message of sympathy to the people of America, particularly those directly affected by the tragedy.

He said: "We would like to extend our sympathy and let them know they are in our thoughts."

The county council is in round-the-clock contact with the police to review security and emergency planning arrangements.

Social workers and teachers are alert to the needs of those who may have been particularly traumatised by what has happened. Anyone wanting to find out about a friend or relative should contact the national hotline on 0207 008 0000.