The US government is to warn its citizens to stay away from high-profile sites in Europe amid renewed fears over al-Qaida terrorist attacks, reports say.
American and UK officials are understood to have been in contact over the possibility of a broad alert being issued as early as today that would have significant implications for tourism across Europe. High-profile tourist sites and transport hubs are expected to be highlighted as potential targets.
People are encouraged to exercise caution rather than cancelling travel plans altogether.
The warning comes one week after intelligence officials in Britain intercepted a credible Islamist-linked terror plot. The attack would reportedly have been similar to the deadly commando-style raids in Mumbai, India, two years ago, with other European cities, in France and Germany, also targeted.
On Tuesday night the Eiffel Tower in Paris was evacuated following a bomb threat called in from a telephone booth. It was the second such alert at the tower in two weeks. A search by bomb experts found nothing unusual, and it was reopened within hours.
There has also been speculation that Osama bin Laden could be masterminding the latest plots personally.
There has been an upsurge in US drone raids in Pakistan in recent weeks as Nato targets Islamic militants. The US has carried out at least 25 drone strikes so far this month in Pakistan's tribal areas – the highest monthly total for the past six years, US media reported.
US officials have been pushing Pakistan to increase their search for al-Qaida militants, who are believed to be hiding in a mountainous border region in the country.