Thousands of pro-Palestinian protesters rallied outside the UK prime minister’s official residence in central London on Tuesday, demanding that Israel cease airstrikes against the Gaza Strip that have killed dozens of people, including children.

They were met by a small counter-demonstration of pro-Israel supporters. Videos emerged of clashes between the two opposing groups and with police after officers tried to separate them. The pro-Palestinian crowd was seen chanting “shame on you” at the pro-Israel counter-protesters.

Meanwhile, British Prime Minister Boris Johnson on Wednesday urged Israel and the Palestinians to “step back from the brink,” calling for both sides to “show restraint” as conflict escalated.

“The UK is deeply concerned by the growing violence and civilian casualties and we want to see an urgent de-escalation of tensions,” he wrote in a tweet.