The German government said Monday it was "ashamed" of weekend demonstrations against the US decision to recognise Jerusalem as Israel's capital which saw some protesters chant anti-Semitic slogans and torch Israeli flags.

Chancellor Angela Merkel's spokesman Steffen Seibert told reporters that although Berlin opposed the move by US President Donald Trump last week, it strongly condemned protests in German cities where "hatred" of Israel and Jews was expressed.

"At certain rallies over the weekend, slogans were chanted, Israeli flags were burned and slander against the state of Israel and Jews in general were spread which were shameful," Seibert said.

"One has to be ashamed when hatred of Jews is put on display so openly on the streets of German cities."

Seibert noted that Germany had a "particular responsibility toward Israel and Jewish people in general" because the Nazis slaughtered six million Jews in the Holocaust.

He said that while Berlin protected a constitutional right to free speech and assembly, that freedom did not cover incitement of racial hatred or violence.

"It is important that we continue to stand up to all of that," he said.

Speaking later after a meeting of her Christian Democratic Union party, Merkel condemned what she called "serious rioting" at the demonstrations.

"We oppose all forms of anti-Semitism and xenophobia -- no differences of opinion, including about the status of Jerusalem, justify such actions," she said.

"The (German) state must use all the means at its disposal to stop this."

German cities including Berlin and Munich saw anti-Israel demonstrations over the weekend.

At a protest late Friday in front of the US embassy in the German capital and again on Sunday in the ethnically diverse Neukoelln district of Berlin, demonstrators burned the Israeli flag.

A spokesman for Berlin police told DPA news agency Monday that the authorities would keep a close eye on any further protests in the coming days for legal infractions.

Seibert said last Wednesday that Merkel "does not support" Trump's decision to recognise Jerusalem as Israel's capital "because the status of Jerusalem can only be negotiated within the framework of a two-state solution".