That U.S. intelligence failed to warn of the test drew sharp questions from Capitol Hill and within the agency.
CIA Director George Tenet announced Tuesday he had appointed a review team headed by retired Adm. David Jeremiah to "determine what lessons can be learned."
In a sign of the urgency the CIA places on the question, Tenet asked that Jeremiah report back in 10 days.
A U.S. intelligence official, who spoke on condition of anonymity, said the initial feedback from satellite imagery specialists was that recent activities looked routine, and there were no clear indicators of an impending test.
Nonetheless, the acknowledgment that the test site was being watched indicates it was a high-priority target of U.S. intelligence. Moreover, India's governing Hindu nationalist party announced in March, before it took power, that it would re-examine the country's longtime moratorium on testing.
"This was a colossal failure on the part of our intelligence community," said Sen. Richard Shelby, R-Ala., chairman of the Senate Intelligence Committee. Shelby's committee planned a hearing Wednesday on India, plus a closed hearing Thursday with top CIA officials.
The Washington Post reported in Wednesday's editions that a U.S. spy satellite picked up clear-cut evidence of test preparations at midnight Sunday, six hours before the blasts. But because no unusual activity had been detected earlier, none of the U.S. intelligence analysts responsible for tracking India's nuclear program were on duty. They did not see the more revealing satellite photos until they arrived at work Monday, after the test had been conducted.
Indian officials were careful to give no indications of the impending tests in talks with U.S. counterparts just days before the blasts.
"I don't believe that any of our officials knew for sure that there was going to be such an announcement," State Department spokesman James P. Rubin said. In meetings Friday in Washington with India's foreign minister, Rubin said, "There were no ... warnings that this was going to happen."
Nevertheless, U.S. officials in those meetings strongly urged India to refrain from any dramatic response to perceived provocations by Pakistan, such as the recent testing of a medium-range ballistic missile.