An Iranian firm closely linked to Tehran's nuclear program acquired special hardware for enriching uranium, despite sanctions intended to keep such equipment out of Iran, according to officials with knowledge of the matter.

In recent weeks, the officials said, an Iranian procurement firm obtained critical valves and vacuum gauges made by a French company that until December was owned by U.S. industrial conglomerate Tyco International. The French and U.S. firms said they knew nothing of the case.

Western authorities are still struggling to understand precisely how the valves and gauges in question reached Iran. The International Atomic Energy Agency is investigating the matter, according to a Vienna-based diplomat, and Western intelligence agencies also are investigating, The Wall Street Journal has learned.

A Jan. 14 e-mail that triggered the IAEA investigation alleged that the valves moved through an intermediary representing a Chinese company based near Shanghai.

The hardware is part of a high-stakes game of cat and mouse played out on a daily basis between Iran and Western authorities determined to frustrate Tehran's nuclear ambitions.

An investigator familiar with the IAEA probe said Iran has made about 10 attempts to acquire valves used in uranium enrichment in the last two years. "Some deliveries got through, others didn't," he said. Other officials said it isn't uncommon for manufacturers' products to land in Iran without the makers' knowledge.

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