WASHINGTON — The Obama administration has concluded that uranium particles discovered last year at a secretive Iranian military base likely were tied to the country’s past, covert nuclear weapons program, current and former officials said, a finding that contradicts Tehran’s longstanding denials that it was pursuing a bomb.

Traces of man-made uranium were found at the Parchin facility, southeast of Tehran, by investigators from the International Atomic Energy Agency, the United Nations’ nuclear watchdog, as part of an investigation tied to the landmark nuclear deal reached last July between Iran and global powers.