German Foreign Minister Sigmar Gabriel said a move by the United States to abandon the Iranian nuclear deal would discourage other powers such as North Korea from participating in international negotiations to end their own nuclear programmes.
Gabriel, speaking on the sidelines of a United Nations meeting, said world powers had every interest in maintaining the 2015 deal and much work would be needed in coming weeks to ensure it remained in force.
"It's an almost tragic situation where the only existing agreement to prevent the proliferation of nuclear weapons is in jeopardy at a time when we are seeing other countries like North Korea acquiring nuclear weapons and we need such processes more than ever," Gabriel said.
Germany helped negotiate the Iran nuclear deal along with Britain, China, France, Russia and the United States.
U.S. President Donald Trump has called the 2015 deal "an embarrassment" but it is supported by the other major powers that negotiated it. Its collapse could trigger a regional arms race.
Gabriel told reporters in New York he agreed with U.S. officials that Iran had not changed its behavior in the Middle East after the agreement was reached – a matter that required attention, but not as part of the nuclear agreement.
"I am convinced that neither the volatile and charged situation in the region, nor Iran's behavior will improve if the nuclear agreement goes out of force," he said. A recording of his remarks was provided to Reuters by the ministry.
Any move by Washington to cancel the agreement would be a "terrible signal" for all other efforts to use diplomacy to halt nuclear weapons programs, such as those of North Korea.
"Because no one has the impression anymore that international negotiations are worth and one has to assume that such an agreement can be cancelled after a short time," he said.
Gabriel said Trump had received no support for his position.
Meanwhile, Chinese Foreign Minister Wang Yi said that the recent tensions on the Korean peninsula underlined the importance of the Iranian nuclear deal.
China supports and safeguards the Iranian nuclear deal, Wang said in a meeting on Wednesday at the United Nations in New York between the foreign ministers of Iran and the six world powers that negotiated the deal, according to China National Radio.
The U.S. president has reportedly determined how he wants to approach the Iran nuclear deal, but Secretary of State Rex Tillerson said Trump has not informed him or others in the administration about his decision.
Tillerson said Trump even refused to share his decision with British Prime Minister Theresa May when she asked about it.
The top U.S. diplomat said that while Iran might be meeting its obligations to the letter of the deal, it is violating its spirit.
"One can almost set the countdown clock to Iran resuming its nuclear activities," Tillerson said.
Tillerson spoke to reporters after a meeting Wednesday evening of the parties to the nuclear deal, including Iranian Foreign Minister Mohammad Javad Zarif