“The group is spread across a large area which makes it impossible to count them,” a Metropolitan Police spokesman said.

“Officers are engaging with a group of people who have gathered for a demonstration in central London this afternoon,” the police said in a separate statement, adding that a plan was in place to curb the spread of Covid-19.

“This time is different. This time we will not be denied any more. We are united. We have had enough of oppression,” Palestinian Ambassador Husam Zomlot told the demonstrators.

“Today we are saying enough, enough with the complicity,” he added.

Israel’s violent escalation in Gaza creates diplomatic headaches for Gulf states that embraced new ties

Simon Makepace, a 61-year-old accountant said he had joined the protests because “the whole world should be doing something about it, including this country”.

He was critical of the US, which he said was unfairly backing Israel, and urged Washington to “make peace and stop what’s happening”.

Azadeh Pyman, a 50-year-old scientist said she had been raised on the Palestinian cause by her parents and grandparents.

“I’m not Palestinian originally but my heart bleeds for Palestinians,” she said. “I think it’s the cause that will go from one generation to another generation, until Palestine is free.”

In Madrid, some 2,500 people, many of them young people wrapped in Palestinian flags, marched to the Puerta del Sol plaza in the city centre.

“This is not a war, it’s genocide,” they chanted.

“They are massacring us,” said Amira Sheikh-Ali, a 37-year-old of Palestinian origin.

“We’re in a situation when the Nakba is continuing in the middle of the 21st century,” she said, referring to the “catastrophe”, a word used by Palestinians to describe Israel’s creation in 1948 when hundreds of thousands fled or were driven out.

“We want to ask Spain and the European authorities not to collaborate with Israel, because with their silence, they are collaborating,” said Ikhlass Abousousiane, a 25-year-old nurse of Moroccan origin.

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Israel sends ground troops and tanks near Gaza, threatening to open a new front in the fighting

Israel sends ground troops and tanks near Gaza, threatening to open a new front in the fighting

The marches came amid the worst Israeli-Palestinian violence since a 2014 war in Gaza.

Thousands marched in Berlin and other German cities following a call by the Samidoun collective.

Three marches were authorised in Berlin’s working class Neukoelln southern district, home to large numbers of people with Turkish and Arabic roots.

The protesters shouted “Boycott Israel” and threw paving stones and bottles at the police, leading to several arrests.

Other protests were held in Frankfurt, Leipzig and Hamburg.

On Tuesday, Israeli flags were burnt in front of two synagogues in Bonn and Muenster.

Police officers used tear gas and water cannon in Paris to try to disperse a pro-Palestine rally held despite a ban by authorities.

Some threw stones or tried to set up roadblocks with construction barriers, but for the most part police pursued groups across the district while preventing any march toward the Place de la Bastille as planned.

“You want to prohibit me from showing solidarity with my people, even as my village is being bombed?” Mohammed, 23 and wearing a “Free Palestine” T-shirt, said.

The march was banned on Thursday over concerns of a repeat of fierce clashes that erupted at a similar Paris march during the last war in 2014, when protesters took aim at synagogues and other Israeli and Jewish targets.

No incidents were reported as thousands of people gathered for protests and marches in several other cities including Montpellier, Toulouse and Bordeaux.

Around 500 people rallied in Athens, AFP correspondents said. Greek police used water cannon and there were minor scuffles with protesters in front of the Israeli embassy.

Gatherings to show solidarity with Palestinians also took place in the United States in cities including Boston, Washington, Houston, Texas and Dearborn, Michigan as well as Montreal in Canada.

Several hundred people turned out in the Bay Ridge area of Brooklyn, New York, chanting “Free, free Palestine” and “From the river to the sea, Palestine will be free.”

They waved Palestinian flags and held placards that read “End Israeli Apartheid” and “Freedom for Gaza.”

Many protesters wore black and white, and red and white, keffiyeh scarves, while drivers sounded car horns and motorcyclists revved their engines as the sun beat down.

Several Jewish people attended, carrying placards that said “Not in my name” and “Solidarity with Palestine” as the protesters took over a street in the area which has a large Arab population.

A few dozen police officers looked on and the protest was peaceful in its early stages.

Israel is fighting Hamas militants in Gaza while trying to contain an outbreak of internal Jewish-Arab clashes and violence in the West Bank.

The Israeli bombardment began on Monday, after Gaza’s Islamist rulers Hamas fired rockets towards Jerusalem.

That was in response to bloody Israeli police action at the flashpoint Al-Aqsa mosque compound in Jerusalem, as well as a crackdown on protests against the planned Israeli expulsion of Palestinians from their homes in the Sheikh Jarrah neighbourhood in annexed east Jerusalem.

Since Monday, Israeli air and artillery strikes on Gaza have killed 139 people including 39 children, and wounded 1,000 more, health officials say.

Palestinian armed groups have fired hundreds of rockets at Israel since, killing 10 people, including a child and a soldier. More than 560 Israelis have been wounded.