Recent terrorist plots to kill U.S. soldiers at Fort Dix in New Jersey and the JFK bomb plot in New York are merely the tip of the iceberg U.S. officials confide.
And officials report that the "chatter" they are monitoring is increasing.
"There's a lot of activity out there," a counterterrorism official told Britain's Daily Telegraph’s Toby Harnden. "Obviously, you don't want to tip off every suspect that they are being monitored. On the other hand, we are not going to wait until the fuse is lit."
U.S. intelligence agencies discovered the JFK plot that provoked an FBI undercover sting operation, when CIA operatives in the Caribbean and South America learned of it nearly 18 months ago. "Our intelligence agencies pay careful attention to what goes on there," an official told The Daily Telegraph.
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"Although a lot of the public focus is on Europe; we're also looking closely at the home-grown threat and what's going on in our own back yard."
Moreover, the two plots were merely a small part of the dozens of other plots now being monitored. The official added that much of the success of the investigations was due to improved cooperation between the CIA and FBI which, the lack of which had been blasted by the 9/11 Commission report.
"The FBI was all over the plot from the start and there was textbook cooperation with other agencies," the official said. "But this shows the threat posed by the unknown terrorist, the person who becomes almost self-radicalized.
"In this modern era, you can quickly gather a lot of information online and also reach out to international networks," he said.
The counterterrorism official told the Daily Telegraph that although the JFK plot to blow up fuel supply tanks and set off a chain reaction all along the 40-mile fuel pipeline that feeds the tanks "was not technically possible," it was just one of many cases being investigated by the U.S. government.
The plot highlighted the twin dangers of Muslim Islamists holding American passports and plots with links to other countries.