The US government is considering warning its citizens to stay away from crowded places in Europe because of the threat of an al-Qaeda commando-style attack, the BBC has learned.
US and UK officials have confirmed that updated guidance may be issued because of the current terror threat.
A UK official said the travel advisory would not be country-specific.
It would also not go as far as advising against travel to Europe, the official said.
The advisory will be issued in response to intelligence on an al-Qaeda plan to assemble teams of gunmen and send them into crowded places to kill western civilians, similar to the 2008 attacks in Mumbai.
After intelligence details of the plan had been leaked to the US media last week, officials said that the plan had not been stopped but that an attack was not expected to be carried out imminently.
Officials said that several individuals were still under surveillance.
The suspects include British citizens of Pakistani and German citizens of Afghan origin.
Recent US drone raids in Pakistan reportedly targeted the al-Qaeda militants who inspired the plans.
US officials said that a travel alert might be issued as early as Sunday.
Such a warning could have negative consequences for European tourism if travellers fear that there is a risk of terror attacks.