Four police officers were injured after pro-Palestinian protesters in London set off fireworks into crowds.
Scotland Yard said a dispersal order was authorised at 6.43pm on Saturday, which remained in place until 1am on Sunday.
More than 1,300 officers were on duty as tens of thousands of people demonstrated in London.
A total of 29 people have been arrested after a protest was held in Trafalgar Square to demand a ceasefire in the Israel-Hamas war.
They were held on suspicion of inciting racial hatred, other racially motivated crimes, violence and assaulting a police officer, the Metropolitan Police said.
Demonstrators climbed on top of the square's famous fountains as the mostly peaceful group waved flags and banners.
But police said some protesters had launched fireworks into crowds and towards officers.
There were scuffles with police as the evening went on, and smaller groups of protesters began moving away from the square.
At least one protester was seen carrying a banner which read "Let's keep the world clean" - with a picture of an Israeli flag being thrown into a bin.
Other protesters chanted "from the river to the sea, Palestine will be free", despite controversy around the slogan's meaning.
Home Secretary Suella Braverman has said the slogan is antisemitic and "widely understood" to call for the destruction of Israel. However, pro-Palestinian protesters have contested this.
Effigies of dead babies were left on the ground in Trafalgar Square, next to pictures of children and candles.
An order was issued giving officers the power to require someone to remove any item being used to conceal their identity, the force said.
Commander Karen Findlay, who is responsible for policing in London this week, said: "The vast majority of people demonstrated peacefully during an extremely busy day in central London, with protests in a number of locations requiring a policing presence.
"It is disappointing that various splinter groups were again responsible for behaviour which has no place in London and we are determined to deal with this robustly."