Iran's foreign minister is warning amid tensions between Washington and Tehran that "whoever starts a war with us will not be the one who finishes it."

Mohammad Javad Zarif made the remarks on Monday, speaking alongside visiting German Foreign Minister Heiko Maas.

Maas is in Tehran in an effort to salvage Iran's 2015 nuclear deal with world powers. Germany is a signatory to the accord.

Zarif came out to a news conference in Tehran grim-faced after a long private discussion with Maas, who on Sunday called Iran's ballistic missile program problematic.

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The U.S. pulled out of Iran's nuclear deal over a year ago. That's the root of the current tensions with Iran. In May, Tehran said it would begin enriching uranium closer to weapons grade if Europe didn't come up with new terms for the deal by July 7.