Biarritz, France (CNN) When Iran's Foreign Minister, Javad Zarif, landed in Biarritz Sunday afternoon it appeared France's Emmanuel Macron, this year's G7 host, had pulled off an end run around his most powerful guest, US President Donald Trump.

For weeks Macron has been pushing Trump to soften his stance on Iran, and Trump has pushed back, last month tweeting: "I know Emmanuel means well, as do all others, but nobody speaks for the United States but the United States itself."

In May last year Trump unilaterally pulled the USA out of the multilateral Joint Comprehensive Plan of Action nuclear deal with Iran, and this year ratcheted up sanctions on the Middle East nation to create "maximum pressure" to have it dial back its "destabilizing" regional activities.

Iran has responded by attacking and detaining oil tankers in the strategic Straits of Hormuz, breaking the terms of the JCPOA and demanding European signatories, France, Germany and the UK do more to make the nuclear deal work.

The vital waterway, through which one fifth of the world's oil passes daily, has become a tinderbox where one wrong move might trigger a regional war.

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