Thousands of pro-Palestinian protesters have marched through central London – a day after the UK joined the US in attacking Houthi bases in Yemen.

The Iran-backed rebel group, which supports Hamas, has been targeting commercial shipping in the Red Sea.

It has vowed to damage vessels it believes are heading to and from Israel until there is a ceasefire in Gaza.

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One speaker in Parliament Square on Saturday said British planes had been “flying where they do not belong”.

A few Yemeni flags were spotted on the march, Sky News correspondent Ivor Bennett said.

One placard read “Hands off Yemen”. According to its bearer, the only way to stop Houthi attacks on shipping in the Red Sea is to support a ceasefire in Gaza.

Another placard read: “UK + US wants war. Yemen supports Palestine. Gaza wants to live.”

Six arrests have been made, two of which were “in relation to offensive placards”, the Metropolitan Police said.

Another three people were arrested on suspicion of showing support for a proscribed organisation – an offence under the Terrorism Act.

One person was held for being in possession of “stickers to be used for criminal damage”.

A “significant policing presence” of about 1,700 officers was planned by Scotland Yard, which handed out leaflets.

The protesters want Israel to stop its military operations in Gaza, which followed the Hamas attacks in Israel on 7 October.

Husam Zomlot, the Palestinian ambassador to the UK, accused the British government of “complicity” with Israel.

Speaking in Parliament Square, he said Palestine was a “nation of freedom fighters”, adding: “I stand before you with a broken heart but not a broken spirit.”

He also congratulated South Africa for bringing a genocide case against Israel at the UN’s International Court of Justice.

That case has “gone down well with demonstrators”, Ivor Bennett said, with one woman saying she was “ecstatic” at the news.

Mary Lou McDonald, the president of Sinn Fein, told the crowd that a better situation for the Palestinian people is possible.

“When I say this, standing in London, in common cause with you, (having) walked our own journey out of conflict, building peace for 25 years, this can happen,” she said.

“This must happen and we will ensure that it does.”

Former Labour leader Jeremy Corbyn addressed protesters in Parliament Square, while his former shadow chancellor, John McDonnell, could be seen leading the march as it left Bank.

There were restrictions, including: any person participating was warned not to deviate from the specified route; the speeches had to end by 4.30pm; the whole event had to end by 5pm.

No participant was allowed to enter the area around the Israeli Embassy.

James Cleverly, the home secretary, said he had been briefed by Met commissioner Sir Mark Rowley on plans to “ensure order and safety” during the protest.

“I back them to use their powers to manage the protest and crack down on any criminality,” he said.