German Chancellor Olaf Scholz said on Thursday Iran bore responsibility for helping Hamas grow to the point where it launched last weekend's attack on Israel, as he announced a crackdown on organisations that backed the Islamist movement.

"While we have no firm proof that Iran operationally supported this cowardly attack, it is clear to us all that without Iranian support, Ham as would never have been able to launch this unprecedented attack," he said.

"The jubilant statements from the top of the Iranian regime and some other government officials in the region are abhorrent. The leadership in Tehran shows its true colours without shame, and thereby confirms its role in Gaza."

The Islamic Republic has celebrated the Hamas assault but denied that Tehran was behind them.

In a special address to the German parliament, Scholz said his government would ban all fundraising and other activities supporting Hamas, including being seen to glorify its actions or displaying its symbols.

He also announced a ban on Samidoun, an international activist group that says it supports Palestinian prisoners in Israeli jails, but which German authorities say promotes hate speech and calls for Israel's destruction.

Samidoun did not respond to a request for comment.

Germany rallied around Israel after at least 1,300 people were killed and dozens taken hostage in a mass cross-border infiltration by Hamas militants into Israeli towns and villages near Gaza. It has frozen Palestinian aid pending a review.

Germany has stepped up protection of Jewish institutions and banned a pro-Palestinian protest due to take place in the capital Berlin on Wednesday.

Like other German leaders, Scholz said the country had a historic duty towards Israel given its responsibility for the Nazi-perpetrated Holocaust.

The suffering of civilians in the Gaza Strip was likely to worsen "but that too is the fault of Hamas and its attack on Israel," Scholz said, while also criticising what he said was the "shameful" silence of Palestinian President Mahmoud Abbas, whose West Bank-based Fatah movement is a rival of Hamas.

Gaza authorities say more than 1,200 people have been killed in a retaliatory Israeli bombing campaign.

Scholz added that it was important to try and avoid a further regional escalation of violence, warning Hezbollah, another Iranian-backed militant group, powerful in Israel's neighbour Lebanon, not to risk an attack on Israel.

"I am in close contact with Egypt's President Sisi, who has channels to Gaza. I will speak with Turkey's President Erdogan today and receive the Emir of Qatar," he added. "All three can play an important role in de-escalating the situation."