The calls are one piece of a growing body of evidence pointing to the presence of suspected members of terrorist sleeper cells operating on U.S. soil and a growing sophistication on their part to keep their communications secret, the officials said.
The officials, who spoke only on condition of anonymity, said the effort to follow the phone call trail has involved numerous federal agencies and is the result of improved post-Sept. 11 coordination between the traditional law enforcement of the FBI and the intelligence gathering of the National Security Agency, the United States' premier overseas electronic intercept agency.
"Things have really improved, and that gives us the ability to better track terrorists both in the United States and abroad and prevent things before they happen," one senior law enforcement official said.
Authorities said the calls point to the clear presence of one or more sleeper cells in the United States and attempts by al-Qaida sympathizers in the United States to make their calls difficult to trace, using tactics invented by U.S. criminals in the 1990s.
With Friday's arrest of five American men of Yemeni descent in a Buffalo, N.Y., suburb, Deputy Attorney General Larry Thompson said that U.S. law enforcement "has identified, investigated and disrupted an al-Qaida-trained terrorist cell on American soil."
U.S. Can Use Bases, Saudi Leader Says
UNITED NATIONS -- In a shift likely to put more pressure on Saddam Hussein, Saudi Arabia's foreign minister said Sunday that U.S. forces may have access to bases in the kingdom to attack Iraq -- provided military action has United Nations endorsement. Prince Saud al-Faisal called on the Baghdad regime to allow U.N. inspectors back into Iraq to ensure it is not developing nuclear, chemical or biological weapons.
Other Arab nations also pressed Iraq to comply with U.N. Security Council resolutions to avert a showdown with Washington, saying they wanted a diplomatic solution to avoid a conflict that could threaten stability in the Middle East. Once international consensus is reached, al-Faisal said, the Iraqis will have to respond or "suffer the consequences."