Protesters in Oregon’s largest city have clashed again with federal agents outside a US Immigration and Customs Enforcement building that has become a new focus of the demonstrations that have gripped Portland for months.

A group of about 100 late on Thursday and before dawn Friday sprayed the building with graffiti, hurled rocks and bottles at agents and shined laser lights at them, Portland police said in a statement.

The agents set off smoke or tear gas and used crowd-control munitions to try to disperse the crowd, The Oregonian reported.

Three people were arrested, police said in their statement.

The violence came a day after protesters clashed with federal agents for the first time since July in a demonstration that also targeted the ICE building. Two people were arrested, and several officers suffered minor injuries.

On Friday, a number of federal buildings across the city were closed as the FBI investigated a car bomb threat.

The agency said in a statement on Friday (local time) that investigators were trying to determine whether the threat, which was reported Thursday, was credible.

It wasn’t clear if the threat was related to the protests.

Violent demonstrations have happened in Oregon’s largest city for more than two months following the police killing of George Floyd in Minneapolis.

On Thursday police released information that showed during more than 80 nights of protests in Portland authorities declared riots more than 17 times and arrested more than 500 people.

The riot declarations allow police to use tear gas, flash bang grenades and other non-lethal weapons to try to break up crowds.

-AP