BERLIN:  Outgoing Foreign Minister Frank-Walter Steinmeier said Germany had fundamental differences with US President Donald Trump about torture and other issues, and warned the US leader against dismantling a nuclear agreement with Iran.

Steinmeier, who will be replaced by Economics Minister Sigmar Gabriel on Friday, told the Sueddeutsche Zeitung newspaper he was "appalled" by the 2016 US election, and could only hope that Trump would change now that he was in office.

"This isn't about little things. It's about fundamental questions in our self-understanding, for instance in the approach to torture," Steinmeier told the paper in an interview published in Friday editions.

The Social Democrat, who is due to become the country's president, a largely ceremonial role, next month, was an outspoken critic of Trump during the campaign and called him a "hate preacher."

Trump drew fire around the world on Thursday after he told ABC television in an interview that he thought waterboarding - a form of simulated drowning that is recognized as torture - "worked" as an intelligence-gathering tool, but would defer to his cabinet on whether to use it in interrogations.

Torture is forbidden under US and international law, and by pacts such as the UN Convention against Torture and the Geneva Conventions.

Steinmeier said he hoped the new US administration would come to see the importance of the transatlantic relationship as the foundation of the West that needed to be nurtured, and the United States would not profit from a weakened Europe.

He also expressed surprise about how little Trump understood about world trade. "Until a few days ago I could never have imagined that a French president and Chinese president would have to instruct their new American colleague about the advantages of an open world and free trade," he said.

He warned against growing nationalism around the world, calling it a "serious and dangerous" threat. "We see that that nothing is irreversible and that even peace in Europe must be continually explained and defended," he said.

Annulling the 2015 Iran nuclear deal would be a grave mistake, Steinmeier said, noting that doing so could trigger a war in the Middle East, which would not be in the interest of the United States or Israel.

"Fears will not be diminished if Iran is once again able to work on nuclear weapons," he said.

Trump, who took office one week ago, has called the Iran accord "the worst deal ever negotiated" and threatened to annul it or seek a better agreement.