Police are at the scene of Sinn Fein's west Belfast offices.
MP Paul Maskey said the Connolly House offices were attacked and damaged overnight in an arson attack on the Andersontown Road property. Paint was also thrown at a window.
He thanked the Fire Service for helping put out the fire.
"Those responsible will not deter our work," he said.
"Last night's disgraceful arson attack on our Connolly House office must be condemned by all.
"This was an attack on the democratic process.
"Clearly the people behind this are intent on trying to disrupt the services we provide to all the public.
"We have not yet been able to assess the extent of the damage but Sinn Fein will continue to provide a first-class service to the people of west Belfast whom we are proud to represent.”
Police said the incident happened at 4.50am.
“Damage was caused to a door at the rear of the building, and to fascia boarding. There was no damage reported to the inside of the building. Paint was also thrown at a front window of the building," Inspector McCullough said.
"This is being treated as arson and I am appealing to anyone who was in the area around this time and noticed any suspicious activity, or anyone who has information which could assist our investigation to contact us on the non emergency number 101, quoting reference 162 of 20/08/18.
"Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”