The revelations underscore the role of Pakistan as a haven for many would-be Islamist militants with foreign ties, a worrying prospect for Western countries who face additional challenges when tracking terror suspects among citizens who have passports and easier access to their shores.
Pakistan, Britain and Germany are tracking the suspects and intercepting their phone calls, the official told The Associated Press. He 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.
"They have been making calls to Germany and London," the official said. "They have been talking about and looking for facilitators and logistics they need there to carry out terror strikes."
Western security officials said Wednesday that a terror plot to wage Mumbai-style shooting sprees or other attacks in Britain, France and Germany was still active. Both European and U.S. officials said the plot was still in its early stages and not considered serious enough to raise the terror threat level.
Still, the Eiffel Tower in ParisTuesday - the second time in two weeks because of an unspecified threat - and there was a heavy police presence around Buckingham Palace, Trafalgar Square and Big Ben.
Although he characterized the plot as immature, the Pakistani official warned against underestimating the suspects, whom he said have backing from al Qaeda, the Pakistani Taliban and the Afghan Taliban, all groups that are separate yet interconnected.
"It does not mean that they are not capable of materializing their designs," the official said. "They are very much working on it."
The official spoke Thursday on condition of anonymity because he was not authorized to release the information to the media. He is part of an intelligence team that has been tracking the two British brothers of Pakistani origin for nearly a year and the Germans for more than six months.
There is ample reason to be wary of the trumpeted terror warnings from European officials, reports CBS News correspondent Mark Phillips. Al Qaeda is not generally in the habit of phoning in warnings about possible attacks as occurred before the Eiffel Tower evacuation, Phillips, and the current alarm seems to be aimed at drumming up support for unmanned drone attacks in Waziristan.
The U.S. has dramatically stepped up its missile attacks in North Waziristan, and is believed to have launched at least 21 this month. The official said a Sept. 8 strike killed one of the Britons, whom he identified as Abdul Jabbar, originally from Pakistan's Jhelum district. Jabbar was believed to be less than 30 years old.
CBS News has learned that the Dept. of Homeland Security's office of Infrastructure Protection sent out an e-mail Tuesday inviting private sector partners to a classified briefing "on recent overseas developments and Homeland threat reporting."
The threat is based mainly on European information and trends of reporting. There is nothing specific regarding times or locations of the attacks. The partner will be told that the concerns involve places of public gatherings such as hotels, parks, sports arenas and shopping mails. The information has the attacks carried out by small units or teams with weapons.
In Brussels on Thursday, Europol director Robert Wainwright said a drop in terror attacks in Europe - coupled with intelligence that had thwarted major plots in the past - masked an ongoing threat.
"There has been a significant decline in the number of terrorist attacks in Europe - certainly committed by Islamist groups - that hides the reality that these groups are still active," Wainwright told AP.
A German intelligence official, speaking on condition of anonymity because he was not authorized to speak with the media, said Germany regularly tracks suspected radicals leaving the country to go to train in Pakistan or Afghanistan, but cannot do anything to prevent them from leaving the country.
When they return, however, German laws enacted since the Sept. 11, 2001, attacks in the United States now allow authorities to charge people for having trained in such camps.
In August, for example, a 25-year-old German citizen identified only as Rami M. was extradited from Pakistan and charged with membership in a terrorist organization. According to prosecutors at the time, he left Germany in March 2009 to join a terrorist training camp in Pakistan, where he learned how to handle "weapons and explosives," prosecutors said when he was charged.
He then joined the Islamic Movement of Uzbekistan's fighting in the region, the prosecutors said. The group is suspected of terror attacks mostly targeting Pakistani security forces or NATO's international troops in Afghanistan, prosecutors said.
French authorities, meanwhile, have received indications from allied intelligence services about the possibility of attacks, but no plot outright, a high-ranking French security official said on condition of anonymity because of the sensitivity of the issue.
A recent spate of anonymous, phoned-in bomb threats in Paris - including on the Eiffel Tower - didn't appear to have the "signature" of al Qaeda, the official said, noting the terror network hasn't typically tipped off authorities to attacks in advance.