Maas is to meet Rouhani and his Iranian counterpart, Mohammad Javad Zarif, as part of a European effort to salvage Iran's nuclear pact with world powers and defuse rising U.S.
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.
"The economic war that Mr. Trump has referred to is economic terrorism in our viewpoint, therefore it should be stopped and (the US) should not disturb our relations (with other countries)", Zarif added.
"Whoever starts a war with us will not be the one who finishes it".
Steps must be taken to avoid war between Tehran and Washington, Germany's foreign minister warned, echoing broader concern in Europe over the fallout of the new standoff in the Middle East.
The accord took effect in January 2016 and was supposed to terminate all nuclear-related sanctions against Iran all at once, but its implementation was hampered by the USA policies and its eventual withdrawal from the deal.
Tensions between Iran and the United States have been simmering since Washington chose to withdraw from the 2015 nuclear deal in May 2018 and reinstated all sanctions against the Islamic Republic. Germany is now a member of the UN Security Council and it is trying to prevent any war, Maas answered to the question of why Germany says it is seeking to reduce tensions in the region while provides weapons to the countries of the region.
The United States pulled out of the 2015 deal - the Joint Comprehensive Plan of Action - a year ago and reinstated its sanctions.More news: Xbox Game Pass Ultimate Discounted to $1; Combines Current Subscriptions
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The relations between the USA and Iran worsened last month, when Tehran announced it will scale back some pledges agreed in 2015 claiming other parties have failed to "live up to their commitments".
Israel has repeatedly warned that Iran is seeking a nuclear arsenal in order to destroy it, and Netanyahu has led global opposition to the 2015 P5+1 nuclear deal with Iran.
Iran has also threatened to scale down its nuclear commitments if its interests are not met. "There is war in Syria and in Yemen, fortunately not here", Maas said. America's John Huddy reports on the increasing tensions. The system uses locally made missiles that resemble the HAWK missiles that the US once sold to the shah and later delivered to the Islamic Republic in the 1980s Iran-Contra scandal.
Maas acknowledged the economic benefits Tehran hoped for from the deal were now "more hard to obtain".
"Europeans are certainly in no position to criticise Iran, even about issues that have nothing to do with" the agreement, Zarif said in televised remarks to journalists.
Maas acknowledged that the economic benefits Tehran hoped for from the deal were now "more hard to obtain" but urged Iran to fully respect the agreement.
France, Germany, and Britain dispatched their diplomats and negotiators to convince the Trump administration otherwise but the message they got in return was that it is non-negotiable. "A financial mechanism called INSTEX has been devised in this respect".