Such a move could have negative implications for European tourism, business and diplomacy if travelers fear there's a possibility of terror attacks.
The State Department will issue a "travel alert" for Europe on Sunday morning that advises Americans to stay vigilant on the continent because of threat information, senior U.S. officials told the AP. The officials spoke on condition of anonymity because a final decision has not been announced.
"This travel alert is a cumulative result of information we have received over an extended period," one senior administration official said. "We are constantly monitoring a range of threat streams and have monitored this and others for some time."
State Department spokesman P.J. Crowley declined to comment on the matter. But he said the administration remains focused on al-Qaida threats to U.S. interests and will take appropriate steps to protect Americans.
A European official briefed on the talks said the language in the U.S. alert is expected to be vague. It won't address a specific country or specific landmarks, the official said.
European and U.S. officials have not identified any specific targets that terrorists might be considering, the official said. Officials have called the threat credible but not specific. Officials have been concerned that terrorists may be plotting attacks in Europe with assault weapons on public places, similar to the deadly 2008 shooting spree in Mumbai, India.
On Friday, Sweden announced it has raised its threat alert to the highest level ever because of an increased threat of terror attacks. But Swedish security officials said there did not appear to be an immediate threat, nor did they cite any possible targets. In Britain, the security level stood at "severe" -- the second highest in a five-step scale -- and there were no plans of raising it further, according to a British security official, who spoke on condition of anonymity because of the sensitivity of the issue.
The U.S. has told European leaders that the State Department alert would be intended to raise the guidance to match the information about the would-be attack that surfaced last week, the European official said.
There had not been strong opposition to the proposed alert from European leaders, the European official said.
But some U.S. allies in Europe expressed concern that the U.S. guidance might include a warning for Americans to stay away from public places in Europe, saying that would be an overreaction to the threat information. Some administration officials agreed and the White House adamantly denied such a blanket warning was being considered.
Intelligence officials believe Osama bin Laden is behind the terror plots to attack several European cities. If this is true, this would be the most operational role that bin Laden has played in plotting attacks since Sept. 11, 2001.
Eight Germans and two British brothers are at the heart of an al-Qaida-linked terror plot against European cities, but the plan is still in its early stages, with the suspects calling acquaintances in Europe to plan logistics, a Pakistani intelligence official said Thursday. One of the Britons died in a recent CIA missile strike, he said. The Pakistani official said the suspects are hiding in North Waziristan, a Pakistani tribal region where militancy is rife and where the U.S. has focused many of its drone-fired missile strikes.
"We remain focused on al-Qaida's interest in attacking us and attacking our allies," Crowley said. "We will do everything possible to thwart them and will take steps as appropriate."
A travel "alert" is less serious than a full "travel warning," which could have big implications. There are hundreds of thousands of Americans in Europe at any one time, including tourists, students and businesspeople.
While the government cannot stop people from traveling there or force them to return home, a formal travel warning could result in canceled airline and hotel bookings as well as deter non-U.S. travelers from going to Europe. In addition, many U.S. college and university study-abroad programs will not send students to countries for which a warning is in place for insurance and liability reasons.
Under a "no double standard" rule, the government is obliged to share threat information that it has given diplomats and other officials with the general public.
The Pentagon declined to say Saturday whether it had increased security levels at any of its European bases.
"As a matter of policy we don't discuss specific force protection measures or levels. Commanders continually evaluate the local security environment and take appropriate and prudent security measures to protect personnel and facilities," said Army Maj.Tanya Bradsher, a Defense Department spokeswoman.
The Italian Interior and Foreign Ministry, German Foreign Office, French Foreign Ministry, Interior Ministry, the national police and the Paris police all declined immediate comment. Calls to the Paris tourism office and the French government's tourist office in the United States went unanswered Saturday and there was no immediate response to e-mail requests for comment.