Protesters hurled shoes towards the US consulate in Edinburgh as a part of a protest against Israeli action in Gaza.
Thousands took part in a rally through the city calling for an end to the military action.
Police said about 4,000 people attended the protest but organisers put the number at 10,000.
About 300 shoes, including ski-boots and clogs, and red paint were thrown as part of the protest. Three police officers sustained minor injuries.
Ch Insp Kevin Greig, of Lothian and Borders Police, said none had required hospital treatment.
He said a criminal investigation had been launched into the incident.
Ch Insp Greig said: "This happened outside the American consulate where the traditional way of displaying discord with what is happening in the Middle East is to take their shoes off and throw them on to the ground.
"Unfortunately a number of these persons, about 60, threw heavy clogs, ski-boots and wooden poles at the police officers."
Asif Dean, from the Scottish Palestine Solidarity Campaign, said he did not see any unrest.
He said: "I was not aware of any trouble at all. The only trouble that I saw was that the police didn't like people voicing their support for Hamas, but I don't think there was any violence or anything. So I'm not aware of any incidents, as far as I'm aware it was a completely peaceful march."
Pete Cannell, secretary of the Scottish Stop the War Coalition, said: "If we'd had a few more days it would've been twice the size."
"The response we got when we were handing out leaflets was overwhelming."
Event organiser Nick Napier said the action was taken as a result of the "rage and anger" over the death toll in Gaza over the past two weeks.
"People are here because they know the trail of blood leads from Gaza back to Britain and that Gordon Brown, while publicly calling for a ceasefire, we know has instructed his diplomats in New York to support the Americans."
He added: "The American position is to endorse Israel's massacre of the people of Gaza.
"That's why we have this unprecedentedly large march here.
"They're angry. It's another year, another war, another massacre.
"It's a war too many for most people."
Hundreds of people also took part in protests in Aberdeen and Inverness.
A spokesman for the American Consulate declined to comment.