Merkel's working trip is last-ditch European effort to prevent a transatlantic trade war and save the Iran nuclear deal.
Ahead of Merkel's visit, France's president Emmanuel Macron tried to persuade Trump to save the pact.
On Wednesday, he called on the United States not to abandon the Iran deal.
Speaking at the US Congress on the final day of a three-day state visit, Emmanuel Macron said the JCPOA was not addressing what he called “all concerns” but stressed that the deal could not be ditched.
Trump has called the agreement, which Germany helped negotiate, "insane" and the "worst deal ever", demanding that its "disastrous flaws" be fixed.The EU and other signatory world powers have sought to convince Trump not to abandon the pact.
Iran has repeatedly warned that any failure to respect the multinational agreement would have grave consequences, stressing that there is no alternative to the nuclear accord.
