Bahrain officials said a city hall was set ablaze during a night of clashes between police and protesters, following the execution of three men convicted of a deadly bombing targeting police.
Bahrain's interior ministry said on Monday that the fire at the Northern City Hall appeared intentional.
It said firefighters were able to contain it.
Hundreds protested on Sunday over the execution by firing squad of three Shia men accused of the 2014 bombing that killed two Bahraini policemen and an Emirati officer.
Abbas al-Samea, 27, Sami Mushaima, 42, and Ali al-Singace, 21 were executed a week after a court upheld their death sentences over the 2014 attack, the prosecution said in a statement carried by the official BNA state news agency on Sunday.
Opponents of Bahrain's Sunni-ruled kingdom saw the men's charges as politically motivated and alleged the men were tortured.
Seven other defendants received life terms.
Some youth threw gasoline bombs and clashed with police into the night on Sunday. Police fired tear gas and birdshot.
In a post on social media, Human Rights Watch's Nicholas McGeehan called the executions "unjust and inflammatory".
"Public, unquivocal condemnation imperative to prevent Bahrain killing more young men," he wrote.
Amnesty International said the executions were carried out "after an unfair trial and despite claims from the men that they were tortured in custody".
Bahrain denies practising torture.
Bahrain's majority Shia population has for decades accused their rulers of discrimination in matters of jobs, housing and political say.
Aljazeera