Germany and France on Saturday moved to reinforce security around Jewish temples, schools, and monuments after the surprise attack by the Palestinian militant group Hamas against Israel.

Germany tightened police protection of Jewish and Israeli institutions, as some supporters of the Palestinians took to the streets of Berlin to celebrate the attack.

France focused on Jewish temples and schools in cities across the country, as one Jewish leader expressed concern at the possibility the conflict might be imported there.

"In Berlin, police protection has been immediately stepped up," Germany's Interior Minister Nancy Faeser told Bild newspaper. "The federal government and the regions are closely coordinating their actions."

Germany's authorities were also closely watching "potential supporters of Hamas in the Islamist sphere", she added.

Berlin police posted photos on social media showing "people celebrating the attacks on Israel by passing out pastries" on Sonnenallee, the main avenue in the city's Neukoelln district.

Police had in some cases carried out identity checks and filed complaints, they added.

The German account of the Samidoun Palestinian Prisoner Solidarity Network posted photos of the distribution of pastries on the streets of Berlin and a message celebrating "the resistance of the Palestinian people".

Martin Hikel, mayor of the Neukoelln district, denounced "a horrible glorification of a terrible war", in comments to Welt television.

He called on the government to ban "the disgusting terrorist propaganda of Samidoun".

Later Saturday, Berlin's famous Brandenburg Gate, a symbol of reunified Germany, was lit up in the colors of the Israeli flag.

"In solidarity with Israel," wrote Chancellor Olaf Scholz on X, formerly Twitter. Israel's ambassador replied on the same platform, thanking him for "this beautiful symbol".

'Shocked and worried'

In France, security had already been stepped up at synagogues in Paris, Marseille, Lyon, and Strasbourg because of religious holidays observed since late September.

Interior Minister Gerald Darmanin sent an urgent message to regional officials asking them to reinforce surveillance even further.

"At a time when terrorist attacks from Gaza are hitting Israel, I ask you to immediately step up vigilance, security and protection of Jewish community sites in France," he wrote in a message seen by AFP.

He called for a "visible and systematic static presence", and the use of soldiers from France's Operation Sentinelle, a special force deployed across the country since the 2015 terror attacks.

The Interior Ministry will review the security situation at a special meeting on Sunday.

In the east of France, increased surveillance of Jewish schools and synagogues in the city of Strasbourg was being organized, said Pierre Haas, of the Council of French Jewish Institutions (CRIF).

"We were very shocked and worried by this outburst of violence," he told AFP.

Knowing the Israeli army would hit back, he said, "we're not reassured by the possibility of the conflict being imported to France".

Police sources confirmed that security had also been stepped up in the southern port city of Marseille, the north of France, and in the Paris region.

London's police service said late Saturday it had increased patrols across parts of the UK capital after "a number of incidents … in relation to the ongoing conflict in Israel and the border with Gaza".

Israeli Prime Minister Benjamin Netanyahu declared that the country was at war after the large-scale, surprise attack launched by Hamas out of Gaza on Saturday.

Hundreds have already been killed on both sides according to figures from Israeli medical services and the Gaza authorities, the conflict's bloodiest escalation in years.