A Homeland Security Advisory System chart shows terrorism threat levels by color.
The Bush administration has raised the national terrorism alert status from yellow to orange, signaling a "high risk" of terrorist attack.
Homeland Security Director Tom Ridge told ABC's Nightline Friday that on a scale of one to 10, the current threat is roughly at "eight."
A government official says Friday's move is based on an increase in information that suggests an attack may occur as Muslims mark the haj, a five-day ritual that begins Sunday.
The move also takes into account U.S. military preparations for a possible war in Iraq.
Orange is the second-most critical level of alarm in the five-tiered system instituted in the aftermath of the Sept. 11 attacks.
Before Friday, the alert level had been at yellow, the middle of the scale. It was raised to orange just once before, for a two-week period surrounding the first anniversary of the attacks.