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Iran could begin producing weapons-grade plutonium by next summer, U.S. and European officials believe, using a different nuclear technology that would be easier for foreign countries to attack.

The second path to potentially producing a nuclear weapon could complicate international efforts to negotiate with Iran’s new president, Hasan Rouhani, who was sworn in Sunday in Tehran. It also heightens the possibility of an Israeli strike, said U.S. and European officials.

Until now, U.S. and Western governments had been focused primarily on Iran’s vast program to enrich uranium, one path to creating the fissile materials needed for nuclear weapons. Now, the West is increasingly concerned Iran also could use the development of a heavy water nuclear reactor to produce plutonium for a bomb. A heavy-water reactor is an easier target to hit than the underground facilities that house Iran’s uranium-enrichment facilities.

Some Iranians and foreign diplomats hope that Mr. Rouhani, a former top nuclear negotiator, will try to negotiate an end to the sanctions that have crippled the Iranian economy. After being sworn in, Mr. Rouhani called on the West to drop the sanctions. “If you seek a suitable answer, speak to Iran through the language of respect, not through the language of sanctions,” he said.

The Wall Street Journal |