LONDON (AFP) - Parts of central London were brought to a standstill on Saturday as thousands of pro-Palestinians marched in protest against Israel's offensive in Gaza, while in Paris a banned demonstration descended into violence.

Organisers of the London rally claimed that "tens of thousands" of people joined the march from Prime Minister David Cameron's office to the Israeli embassy, many of them chanting "Israel is a terror state".

Police refused to give an estimate for the number present but several roads through the centre of the capital were closed during the three-mile (4.8-kilometre) march, which passed off peacefully.

In Paris, by contrast, clashes broke out after hundreds gathered in defiance of a ban on their demonstration, with crowds throwing stones and bottles at riot police, who responded with tear gas.

Some 33 people were arrested by early evening, a police source said, while three police officers were injured in the disorder near Montmartre in the north of the French capital.

Twelve days of violence between Israeli forces and Hamas has seen more than 340 Palestinians killed in Gaza, the majority of them civilians, as well as five Israelis.

In London, demonstrators held up placards pleading for Israel to end its attacks on Gaza, and reading "Stop the bombing, free Palestine" and "End Israeli apartheid".

Opposition Labour lawmaker Diane Abbott said it was the "biggest London Palestinian rally in years".

The left-wing Stop the War Coalition, one of the organisers of the march, condemned British and US support for Israel as "nothing less than collusion with war crimes killing women, children and disabled people".

Sarah Colborne, director of the Palestine Solidarity Campaign, said the five-hour demonstration was a "chance to say enough is enough: Israel's siege of Gaza and its occupation of Palestinian land has to end now".