Pro-Palestine protesters have covered County Hall in red paint and accused the council of being associated with an Israeli defence contractor.
A spokesperson for Somerset Council said: “We believe this incident relates to a legacy commercial investment by Sedgemoor District Council which we have already agreed to dispose of.
"While we respect the right of individuals and groups to protest, we strongly condemn this criminal damage on a Grade II listed public building which will need to be removed at taxpayers’ expense."
The Palestine Action group had claimed the council owned the British headquarters of Elbit Systems in Bristol, which manufactures weapons for the Israeli armed forces.
A spokesperson for the group accused the council of having ‘blood on its hands’, saying: “By taking Elbit's money, our council have Palestinian blood on their hands. By default, they've made the whole county of Somerset complicit in the ongoing genocide in Gaza.
“We refuse to stand by whilst the council continue to ignore our requests to evict Elbit. For the Palestinian people at the other end of Elbit's weapons, we will continue to take action until the council kick Elbit out of Aztec West 600."
Palestine Action said they believed the council should go further than selling the building, and evict the firm from the property, saying the authority would remain on the group’s database of companies and institutions who “profit from and enable Israel’s weapons trade.”
It comes after the group plastered blood-red handprints over County Hall and graffitied the words “Elbit out” across the building.