Four people were arrested when police forced their way into a council-owned property which was being used by squatters in Bristol.
Officers seized a number of items including what Avon and Somerset Police described as “possible petrol bombs”.
Officers closed off Cheltenham Road, Stokes Croft, before entering the building shortly after 2100 BST on Thursday.
Three of the four arrested were detained for public order offences.
Police said another person was arrested on suspicion of threats to cause criminal damage with intent to endanger life.
Supt Ian Wylie said that following the operation it was “unfortunate a small minority gathered and began attacking officers with bottles and other items”.
He added: “There have been several significant incidents in this building during the past few days, which have caused serious concerns to police and local residents.
“The safety of the public is paramount in a situation of this kind and we took the decision to carry out a robust and swift operation, following intelligence received about the criminal intentions of those who were occupying the building.”
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