German Chancellor Angela Merkel voiced a feeling of "deep shame" during her first-ever visit on Friday to the hallowed grounds of the former Nazi German death camp of Auschwitz-Birkenau, where Adolf Hitler's regime murdered more than a million people.

Merkel noted that her visit comes amid rising anti-Semitism and historical revisionism and vowed that Germany would not tolerate anti-Semitism. She said Germany remains committed to remembering the crimes that it committed against Jews, Poles, Roma and Sinti, homosexuals and others.

Chancellor Angela Merkel's government reached a deal Friday on a broad climate plan for Germany, a coalition source said, as tens of thousands of protesters rallied demanding more environmental protection.

Thousands of civil society activists are to mount a march against hate and racism on Saturday in Dresden, a week before state elections when far-right party AfD is projected to make huge gains.

Iran's seizure of a UK-flagged tanker in the Strait of Hormuz has further heightened tensions in the Gulf region after the US military claimed it had downed an Iranian drone.

The far-right Alternative for Germany, battling stagnant poll results and suspicions of illegal funding, is now torn by a deepening rift between its party leadership and its most radical wing.

The turbulence comes as falling migrant arrivals have deprived the ultra-nationalist protest party of its main rallying cause, while the ascendant Greens have replaced them as the strongest opposition force.

Berlin said Monday it had no plans to send ground troops to Syria, refusing a US request for Germany to ramp up its military involvement in the fight against IS militants.

"When I say that the government intends to continue with its ongoing measures in the framework of the anti-IS coalition, then that means no ground troops," said German government spokesman Steffen Seibert.

A 100-kilogramme (220-pound) US World War II bomb was defused overnight near Berlin's central hub of Alexanderplatz, police said Saturday.

Iran's conservative press Tuesday mocked the EU's position on a 2015 nuclear deal abandoned by Washington, accusing Germany's foreign minister of exhibiting both impotence and high-handedness during talks in Tehran.

Since US President Donald Trump quit the agreement in May last year, the European Union has repeatedly renewed its own commitment and pledged to reward Iran's compliance with the sanctions relief promised under the deal.

German Chancellor Angela Merkel's favoured successor Annegret Kramp-Karrenbauer sparked outrage on social media on Tuesday with an apparent call for limits to free speech around elections. 

Germany's government commissioner on anti-Semitism has warned Jews about the potential dangers of wearing the traditional kippah cap in the face of rising anti-Jewish attacks. 

"I cannot advise Jews to wear the Kippah everywhere all the time in Germany," Felix Klein said in an interview published Saturday by the Funke regional press group.