Attorney General John Ashcroft announced at a news conference the increase in the threat level to orange, meaning a "high risk" of terrorist attack, from yellow, the middle level of the five-color system.

He said the decision came after a growing number of intelligence reports warned of the possibility of terrorist attacks on American targets this month.

Ashcroft said the government had received intelligence information, corroborated by multiple sources, that al-Qaeda network sought to attack Americans in or around the end of the Haj, a five-day Muslim religious period which begins Saturday.

The increase in terror threat level triggered tighter government security. Officials also urged greater vigilance by all Americans.

Ashcroft said the intelligence indicates that al-Qaeda operatives might attempt to attack lightly secured targets such as apartment buildings and hotels and that such attacks could involve chemical, biological or radiological devices.

He said there are indications that al-Qaeda might also attack economic targets, such as transportation and energy sectors, as well as symbolic targets of American power.

Officials said the intelligence was coming from intercepts, detainees, foreign intelligence and other sources. They have been particularly concerned about the use of a so-called "dirty bomb" that could spew radiation over a relatively confined area, but there was also the possibility of conventional explosives or even assassinations.

A few hours after the announcement, the FBI issued an alert to law enforcement agencies and the public for help in finding a Pakistani man identified as Mohammed Sher Mohammed Khan, 36, who it said may have entered the United States illegally after Sept. 1, 2001.

The FBI said it had no specific information that Khan was a terrorist, but local media reports quoted an FBI official as saying that Khan was "one of a number of factors" that led to the increase in the threat level.

President George W. Bush approved the decision, which had been debated by senior officials for several days, in a meeting with Ashcroft and Homeland Security Secretary Tom Ridge earlier Friday.

The increased security came as the United States prepared for a possible war against Iraq, but several officials said the US military buildup in the Gulf region was a lesser factor in the decision.

Orange is the second-highest alert level on a five-point scale of risk developed after the Sept. 11 attacks. The highest level is red, representing a "severe" risk.

The last time the Bush administration raised the alert level from yellow to orange was on Sept. 10, 2002, one day before the first anniversary of the Sept. 11, 2001, terror attacks. It was lowered two weeks later.

(Xinhua News Agency February 8, 2003)