Israel's President Isaac Herzog on Wednesday urged Europe to fight anti-Semitism "at all costs", in the face of a worrying increase in hatred being spread notably online.

"The picture is very deeply troubling, anti- Semitic discourse festers not only within dark regimes but within the heartland of the free democratic West," Herzog said in a speech to the European Parliament to mark Holocaust Remembrance Day.

"Jew-hatred still exists. Anti-Semitism still exists. Holocaust denial still exists."

Herzog pointed to reports showing rising incidents of anti-Semitism, especially online where it was "spreading at a record pace at the click of a button".

"I call on you, elected officials of Europe: do not stand by, you must read the warning signs, detect the symptoms of the pandemic of anti-Semitism and fight it at all costs," he said.

An EU report in November said that disinformation and hatred against Jews has "flourished" online throughout Russia's invasion of Ukraine, further aggravating a trend set in motion during the Covid-19 pandemic.

Experts have highlighted the risk of "fake narratives" stoking anti-Semitism, as Russia seeks to justify its war by misusing terms such as "Nazi" and "genocide" to describe the government in Ukraine.

The EU's executive arm presented the 27-nation bloc's first-ever strategy to combat anti-Semitism in October 2021 as Jews in Europe reported increases in hatred.

Herzog also warned European politicians against conflating criticism of Israel with negating "the very existence of the State of Israel".

"Casting doubt on the nation-state of the Jewish people's right to exist is not legitimate diplomacy," he said.

"It is anti-Semitism in the full sense of the word and it must be thoroughly uprooted."

EU countries have divergent approaches to Israel and the bloc often struggles to form a united stance on the conflict with the Palestinians.

The EU and Israel last year restarted meetings of a joint council after a decade-long pause caused by Israeli anger at Brussels' criticism of expanding West Bank settlements, which are illegal under international law.

But the return of Benjamin Netanyahu as prime minister at the helm of the country's most right-wing government ever has dimmed hopes of improving ties.

Herzog, a figurehead president, called on EU nations to "broaden and deepen and strengthen our partnership".

"We must work together as a single community, determined and cohesive against the forces of darkness and hatred that threatened to destroy us," he said.

He singled out the threat from Israel's arch-foe Iran, for not only wanting to eliminate his country, but also cracking down on demonstrators at home, arming Russia in its war on Ukraine and seeking nuclear weapons.

The EU is in charge of mediating efforts to revive a 2015 deal with Iran on its nuclear programme, which Israel fiercely opposes, but the push to rescue the accord has stalled.