(CBS) The government raised its terror threat level to "high risk" orange on Friday, warning of a growing possibility that Osama bin Laden's al Qaeda network would launch an attack against the United States to coincide with Muslim holy days.

Changing the terror alert color from "yellow" triggered tighter government security. Officials also urged greater vigilance by all Americans.

Evidence that something big is going on has been mounting for weeks, reports CBS News Correspondent Jim Stewart, especially in Europe where police in Italy and Spain recently broke up suspected al Qaeda cells apparently on the verge of launching attacks.

In the past two days, the White House has been briefed on what one U.S. official called "increasingly scary stuff" suggesting more terrorist cells were about ready to go operational as well.

Altogether, it was more than enough, officials felt, to raise the national terror alert status.

"Recent reporting indicates an increased likelihood that al Qaeda may attempt to attack Americans in the United States and or abroad in or around the end of Hajj, a Muslim religious period ending mid February 2003," said Attorney General John Ashcroft, who announced the change at a Justice Department news conference along with Homeland Security Secretary Tom Ridge and FBI Director Robert Mueller.

Last year during Hajj, the annual Muslim pilgrimage to Mecca in Saudi Arabia, officials did not raise the alert level. But this year it comes as the U.S. prepares to go to war in the region against Iraq and officials believe terrorists may want to capitalize on the twin timing.

U.S. officials say the greatest number of specific threats is aimed at U.S. troops in the Persian Gulf; at targets inside Europe, including Great Britain; plus Washington, D.C., and the greater U.S. East Coast.

Ashcroft also repeated a warning the FBI voiced last year about the most likely targets.

"Recent intelligence reports suggest that al Qaeda leaders have emphasized planning for attacks on apartment buildings, hotels and other soft, lightly secured targets in the United States," he said.

Going from yellow to orange automatically kicks in several additional layers of security, mostly at points of entry to the United States. Airports, where new technology to examine checked baggage has eased some concerns, were also beefed up; and military bases in the U.S. were ordered to a higher alert level.

"For individual Americans, we ask you to remain aware and remain alert. We are not recommending that events be cancelled and travel or other plans be changed," said Ridge.

U.S. officials say the latest intelligence does not come from any newly captured al Qaeda leaders or anyone else in custody. Most of it, they said, originates overseas. Some of it is extremely specific, and all of it, they conclude, suggests that al Qaeda has moved from scouting targets to preparing to hit them, reports Stewart.

"It's their intention to do what they can to disrupt free people and destroy the values for which America stands and which it represents so prominently to the world," Ashcroft said.

A few hours after the announcement, the FBI issued an alert to law enforcement 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 — his name and birthdate might be fictitious — but that agents want to question him.

An FBI official, speaking on condition of anonymity, said Khan was not the reason the terror alert level was raised but that he was "one of a number of factors."

The U.S. military buildup for possible war with Iraq was a lesser factor in the decision to raise the U.S. threat level, several officials said.

But Rep. Dennis J. Kucinich, D-Ohio, a leading congressional opponent of war with Iraq, said the change provided evidence that "this march to war, far from making our nation more secure, has raised the threat to Americans."

The decision was approved earlier in the day by President Bush during an Oval Office meeting with Ashcroft and Ridge, who had been going over new intelligence in the White House situation room.

"I agree. Change the code," Mr. Bush was quoted as saying by spokesman Ari Fleischer.

Orange is the second-highest alert level on a five-point scale of risk developed after the Sept. 11 attacks. The level was last that high in September and stayed there for two weeks to coincide with the first anniversary of the attacks. The highest alert level is red, which signals an imminent attack.

The State Department issued a worldwide alert Thursday for Americans overseas about the threat, warning of the possibility of suicide bombings, kidnappings or assassinations.

The FBI was providing some details about the threat increase to 17,000 police agencies nationwide and to its Joint Terrorism Task Forces — made up of federal, state and local law enforcement personnel — across the country. Ridge also talked with business leaders who run the nation's key infrastructure, such as electric power grids, dams, financial networks and transportation systems.

Government officials have grown increasingly concerned about the likelihood of terrorist attacks within the United States as intelligence sources are reporting an increase in terrorist activity or "chatter." One official said this activity was rivaling that seen before the Sept. 11 terror attacks.