Tens of thousands of people turned out on central London's streets on Saturday for a pro-Palestinian march calling for a permanent cease-fire in Gaza.
At least five people were arrested on suspicion of inciting racial hatred, police said.
The National March for Palestine was the latest of several huge protests staged in the British capital and many European cities every weekend since the Israel-Hamas war began last month.
Saturday's protests came on the second day of a four-day cease-fire that has allowed critical humanitarian aid into the Gaza Strip and given civilians their first respite after seven weeks of war.
The Metropolitan Police said officers arrested a man on suspicion of inciting racial hatred "near the start of the protest." The man was spotted carrying a placard with Nazi symbols on it, police said.
Later Saturday, police said they arrested four more people who distributed "literature featuring a swastika inside a Star of David."
Officers handed out leaflets at the march that sought to clarify what would be deemed a criminal offense, after the force faced pressure from senior government officials to be tougher on alleged displays of antisemitism at the protests.
"Anyone who is racist or incites hatred against any group should expect to be arrested. As should anyone who supports Hamas or any other banned organization," said Deputy Assistant Police Commissioner Ade Adelekan. "We will not tolerate anyone who celebrates or promotes acts of terrorism – such as the killing or kidnap of innocent people – or who spreads hate speech."
The force said 1,500 officers were deployed to police the march.
Hizb-ut-Tahrir, the Islamist group, also protested Saturday outside the Egyptian Embassy in London. Police said two women who were seen holding offensive placards were arrested for a racially aggravated public order offense.
In Paris, a march staged for the International Day for the Elimination of Violence against Women drew both pro-Palestinian and pro-Israeli activists as well as other groups.
Some protesters, waving Palestinian flags and posters reading "Free Palestine," walked in a show of solidarity with "Gaza and Palestine's women who are being murdered."
A group of Jewish women also joined the march to denounce crimes committed by Hamas, including rapes and killings, chanting, "We are women, we are proud, we are Jewish and we are angry."
Meanwhile, some pro-Palestinian protests were organized over the weekend in France's major cities including Strasbourg, Lyon and Marseille.
In Vienna, many marched amid the first snow in the city, waving Palestinian flags at a "Peace for Palestine" rally. Organizers called on the Austrian government to back a cease-fire in Gaza, the release of all Israeli hostages and Palestinian prisoners, and the lifting of the Gaza blockade.
Organizers warned potential participants ahead of Saturday's demonstration that any antisemitic or far-right actions would be "stopped immediately" and offenders would be asked to leave the event.
Tens of thousands of people are also expected to take part in a march organized by the Campaign Against Antisemitism charity on Sunday to show solidarity with the Jewish community in the U.K.
