Around 500 lawmakers from Britain, France and Germany on Thursday urged the US Congress to save the Iran nuclear deal ahead of a possible US withdrawal next month.

"It is the US's and Europe's interest to prevent nuclear proliferation in a volatile region and to maintain the transatlantic partnership as a reliable and credible driving force of world politics," European lawmakers from across the political spectrum wrote in a letter to their US counterparts.

The Trump administration has demanded that the 2015 nuclear accord be fixed by May 12; otherwise, the United States may reinstate sanctions on Tehran and effectively kill the accord despite Iran's compliance. 

Read more: What are Donald Trump's objections to the Iran nuclear deal? 

The lawmakers from the three European countries that were signatories to the deal warned that abandonment of the nuclear accord would end controls on Iran's nuclear program and create a source of conflict in the Middle East. 

Thirteen years of negotiations with Iran allowed the international community "to impose unprecedented scrutiny on the Iranian nuclear program, dismantle most of their nuclear enrichment facilities, and drastically diminish the danger of a nuclear arms race," they said in the letter published in major newspapers on Thursday and Friday.

"Not a drop of blood was spilt," they wrote.

A US withdrawal would create "lasting damage to our credibility as international partners in negotiation, and more generally, to diplomacy as a tool to achieve peace and ensure security."

Read more:What is the Iran nuclear deal?

Merkel, Macron to lobby Trump

German Chancellor Angela Merkel and French President Emmanuel Macron will head to Washington next week to press the Trump administration to stay in the accord signed by the three European powers, Russia, China and the United States.

A US withdrawal would open a deep divide between the United States and Europe, despite common concern over Iran's ballistic missile program and its support for Syrian President Bashar Assad.

Read more: EU extends Iran human rights sanctions by a year 

The European MPs said that although they "share the concerns expressed by many vis-à-vis this Iranian behavior, [they] are deeply convinced that these issues must be treated separately" outside of the nuclear accord.

Iranian Foreign Minister Mohammad Javad Zarif on Thursday warned that Tehran had several options if the United States leaves the nuclear deal. 

"Tehran's reaction to America's withdrawal of the deal will be unpleasant," he said in New York.

Read more: Iran nuclear deal under pressure as Pompeo heads to State Department

Iranian leaders have signaled that Tehran's response to a US withdrawal would be dictated by the stance of European powers, especially ensuring that Iran benefits sanctions be lifted under the nuclear accord.

European governments led by Britain, France and Germany are considering taking non-nuclear related sanction action against Iran over its ballistic missile program and support for the Syrian regime in order to appease the Trump administration in a bid to save the nuclear accord.

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