People gather with placards to take part in a 'March For Palestine,' part of a pro-Palestinian national demonstration, in London on Saturday. AFP

Attendees, who marched through the heart of the British capital as well as Manchester in northern England, Edinburgh in Scotland and other cities, were shadowed by a heavy police presence.

In London, demonstrators massed neared BBC News' headquarters before an afternoon rally near Prime Minister Rishi Sunak's Downing Street office and residence.

Some held Palestinian flags and placards — bearing slogans including "freedom for Palestine," "end the massacre" and "sanctions for Israel" — as they made their way towards the end-point for planned speeches. Chants of "Rishi Sunak, shame on you" could be heard.

"I think all just people around the world, not just in Britain, must stand up and call for this madness (to end)," Ismail Patel, chairman of the Friends of Al Aqsa campaign, told AFP at the demonstration in the capital. "Otherwise, in the next few days, (we) might see a catastrophe unfolding."

People gather with placards to take part in a 'March For Palestine,' part of a pro-Palestinian national demonstration, in London. AFP

The rallies come as Israel intensifies its war to destroy Hamas' capability, relentlessly pounding the Gaza Strip and deploying tens of thousands of soldiers nearby ahead of an expected ground offensive in the enclave.

That follows last Saturday's attack by Hamas, which saw hundreds of its fighters cross the Israeli border to take hostages and kill more than 1,000 civilians on the streets, in their homes and at a rave party.

'Message'

Ahead of the London protest, the city's Metropolitan Police Service said it would deploy more than 1,000 officers, as the events thousands of miles away reverberate in Britain and elsewhere.

Police and the government have noted a spike in UK anti-Semitic crime and incidents since the Hamas assault, while officers in Sussex, southeast England, arrested a 22-year-old woman on Friday suspected of having made a speech backing Hamas.

A protester lets off a smoke canister walking down Regent Street as they take part in a 'March For Palestine,' in London. AFP

The Met said this week that general expressions of support for Palestinians, including flying the Palestinian flag, were not criminal offences but reiterated that supporting Hamas is a crime.

Ferouza Namaz, 34, a student from Uzbekistan, joined the London protest, arguing that civilians in Gaza are "absolutely innocent." "Just being Palestinian does not give the rights to kill them. These appalling atrocities have been taking place for so many years," he added.

Agence France-Presse