Germany wants to preserve a nuclear deal with Iran because U.S. President Donald Trump did not offer an alternative to halt the Islamic Republic from making atomic weapons after he pulled out of the agreement, Foreign Minister Heiko Maas said on Wednesday.

"The deal is working. We want to keep in place the controls and transparency rules," Maas said during a news conference.

"This is especially so given that it is totally unclear what the U.S. envisages as an alternative to the deal that prevents Iran from developing nuclear weapons while being able to verify compliance."