The warning came as French officials were put on alert for possible terror attacks. British officials, too, have been aware of a possible attack but the terror threat warning has not changed from "severe."
"There have been a succession of terror operations we've been dealing with over recent weeks but one to two that have preoccupied us," said one British government official who spoke on condition of anonymity because of the sensitivity of his work. "Still, it hasn't been to the degree that we have raised the threat level."
Another British official, who spoke on the same terms, would not confirm the plot was "al-Qaida inspired" but said there was an "Islamist connection" and that the plots were in an early stage. No other details were given.
Since the Sept. 11 terror attacks in the United States nine years ago, the terror group has moved outside of Afghanistan and Pakistan to other countries such as Somalia and Yemen.
German officials denied Tuesday they had intercepted threats, saying there had been no change to their threat level.
In Washington, a Western counterterrorism official said some missile strikes in a recent surge of attacks by unmanned U.S. drones in Pakistan were aimed at disrupting suspected terrorist plots aimed at Europe.
It wasn't known whether the drone attacks were related specifically to the plot that European authorities said they had intercepted.
The counterterrorism official said the targeted strikes were aimed at al-Qaida and other militant groups arrayed in Pakistan's tribal region near the Afghanistan border. The official spoke on condition of anonymity because the details of the terror plot remain sensitive.
The Obama administration has intensified the use of drone-fired missiles in Pakistan's border area but this month there have been at least 21 attacks, more than double the highest number fired in any other single month.
A suspected U.S. missile strike on Tuesday killed four militants in northwest Pakistan's South Waziristan region, just across the border from Afghanistan, intelligence officials said. There was no word on the identities of those killed in the attack.
The counterterrorism official, who is familiar with the drone strikes and the details of the Europe terror plots, said Tuesday that the missile strikes in Pakistan are "a product of precise intelligence and precise weapons. We've been hitting targets that pose a threat to our troops in Afghanistan and terrorists plotting attacks in South Asia and beyond."
In Paris, French police on Tuesday closed off the surroundings of the Eiffel Tower, France's most visited monument. Officers pulled red-and-white police tape across a bridge leading over the Seine River to the monument. Officers stood guard.
Bomb experts combed through the 324-meter (1,063-foot) tower and found nothing unusual, the Paris police headquarters said. Tourists were let back inside about two hours after the structure was emptied.
Jean Dupeu, a 74-year-old Paris retiree, had planned to go to dinner in the tower but found himself looking for another restaurant.
"It's surely a bad joke," he said of the threat, adding, "Now is not a good time."
National Police Chief Frederic Pechenard said last week that authorities suspect al-Qaida's North African branch of plotting a bomb attack on a crowded location in France. His warning came after al-Qaida in the Islamic Maghreb, or AQIM, claimed responsibility for the Sept. 16 abduction of five French nationals and two Africans in northern Niger.
The French parliament voted this month to ban burqa-style Islamic veils in France, a subject that has prompted warnings by AQIM. Counterterrorism officials say that is just one of several factors contributing to the heightened threat.
At the Eiffel Tower, an anonymous caller called in a warning to firefighters, the Paris police headquarters said. The company that runs the monument asked police to evacuate it.
Police responded to a similar false alert at the tower on Sept. 14, also following a phone threat. On Monday, the bustling Saint Lazare train station in Paris was briefly evacuated and searched.
As soon as the latest bomb alert ended, huge lines of eager tourists immediately formed under the tower.
Mike Yore, 43, of Orlando, Florida, was among those waiting in line at the 121-year-old iron monument.
"There's no bomb that can blow this thing up," he said.
--- Associated Press writers Elaine Ganley in Paris and Adam Goldman in Washington contributed to this report.