US on high terror alert

Last-minute Christmas shoppers in New York today braved heavily armed police as well as the crowds amid fears of a new terrorist attack.

Teams of specialist "Hercules" officers were joined by Cobra chemical and biological and chemical weapons detection squads for the morning rush-hour.

Millions of travellers across the US also faced long delays at airports amid tighter security.

Security officials in Washington say raising the alert from "high" to "elevated" came after they picked up talk among terrorists about a "spectacular".

US homeland security chief Tom Ridge warned that risk in the near future was "perhaps greater now than at any time since September 11, 2001".

It is the fourth time the US government has raised the colour-coded alert from yellow to orange.

New York has remained on orange alert since the attack on the World Trade Center, but the decision to warn the entire country means extra security measures in the city for the rest of the Christmas holiday.

Officials say they are particularly concerned about the risk of another attack using passenger jets.

Mayor Michael Bloomberg said there had been no specific threats to the city. The traditional New Year's Eve celebrations in Times Square would go ahead as planned.