Three-six people involved in each hijack

US Attorney General John Ashcroft has said that each of the four planes involved in yesterday's crashes at the World Trade Centre was hijacked by between four and six individuals.

"They were armed with knifes and box cutters. Some made bomb threats. A number of the hijackers were trained as pilots in the United States.

"We have credible evidence to suggest that the White House and Air Force One were targets.