Pro-Palestinian demonstrators have marched through central London, with protesters calling for an immediate ceasefire in Gaza and an end to the escalating conflict in the Middle East.

Tens of thousands have walked from Russell Square to Whitehall, where speeches were taking place outside Downing Street.

The event has been organised by groups including the Palestine Solidarity Campaign, with people travelling from around the country to take part.

Fifteen people have been arrested, the Metropolitan Police said.

The protest comes one year after the 7 October attacks in Israel.

The Metropolitan Police said it was hard to accurately estimate turnout but the protest “appears to be greater than other recent protests”.

The crowd stretched from Downing Street to Trafalgar Square while speakers were addressing demonstrators.

People could be seen carrying Palestinian flags and placards with message “ceasefire now” and “hands off Lebanon”, and chanting “stop the bombing now”.

A counter-protest also took place on Saturday afternoon, forcing police to form a cordon between the two marches.

But a small group broke away from the pro-Palestinian protest and were stopped trying to approach the counter-protest at Aldwych. Three people were arrested after officers intervened.

Conditions were imposed to move the counter-protest group back to Trafalgar Square as it got “too close to the main march and well away from the agreed area”, police said.

Police said 15 arrests had been made: three for assaulting an emergency worker, one for supporting a proscribed organisation, three for assault, seven for public order offences and one for breach of Public Order Act conditions.

The force also said it was aware of social media posts showing people holding placards with messages of support for Hezbollah – proscribed as a terrorist organisation by the UK government and others – and it was working to find those involved.

Separately, pro-Palestinian supporters were walking through the centre of Edinburgh on Saturday afternoon.

On Sunday, a memorial event will take place in Hyde Park organised by the Board of Deputies of British Jews, the Jewish Leadership Council and other groups.

The war began when Hamas gunmen attacked Israel on 7 October last year, killing about 1,200 people and taking 251 others as hostages.

Israel responded with a military campaign in Gaza that has now killed at least 41,825 people, according to the Hamas-run health ministry.