German Foreign Minister Heiko Maas on Monday said that he was confident of reaching a deal to save the 2015 nuclear accord with Iran "in the coming weeks".
"We think [the talks] can reach their goal," he said in Madrid after a gathering of the Stockholm Initiative, a group of 16 states working towards nuclear disarmament.
"I think we'll get there in the coming weeks," Mr Maas said.
The talks with Iran resumed in April in Vienna.
The negotiations aim to save the deal between Iran and the five permanent UN Security Council member states, plus Germany.
In 2018, under the administration of former president Donald Trump, the US walked away from the accords designed to prevent Iran from developing a nuclear weapon.
After the Stockholm Initiative meeting in Madrid, member countries "renewed their appeal to all states possessing nuclear weapons ... to promote disarmament by adopting significant measures" to comply with the global Non-Proliferation Treaty, they said.
Stockholm member states' foreign ministers were meeting before the next review conference on the treaty, which has been delayed until early next year because of the coronavirus pandemic, Spanish Foreign Minister Arancha Gonzalez Laya said.
The initiative's members include current co-chairs Germany, Spain and Sweden, as well as Argentina, Canada, South Korea, Ethiopia, Finland, Indonesia, Japan, Jordan, Kazakhstan, Norway, New Zealand, the Netherlands and Switzerland.
