Martin McGuinness has blamed the UVF for a petrol bomb attack on an Alliance Party office in east Belfast.
Seven explosives were thrown at the premises on the Newtownards Road and detectives are reviewing CCTV security camera footage showing four people were involved.
Scorch damage was caused to the building and windows smashed, but no-one was injured.
The office has been targeted repeatedly since a vote on the flying of the union flag at Belfast City Hall in December 2012.
Sinn Fein Deputy First Minister Mr McGuinness said: "The activities of the UVF in east Belfast over the course of the last two years have been particularly disgraceful - criminality of the worst kind.
" The response of unionist political leaders to the activities of these people has been inadequate and I also think the response of the police has been inadequate."
He added: "The people behind this are blatant criminals and their attempt to intimidate and terrorise the local community and elected representatives is futile."
DUP First Minister Peter Robinson said Tuesday night's attack was senseless.
"Destruction of any kind advances no cause and it can never be justified," he said.
"I may not agree with the Alliance Party on many issues but I defend their right to pursue their politics through the democratic process.
"I hope that those responsible for this attack are apprehended and face the full weight of the law."
East Belfast Alliance MP Naomi Long said it was "another attack on democracy".
"If there are still people out there who think that violence and intimidation will prevent Alliance from working on behalf of the public in east Belfast, they are absolutely and totally wrong.
"My colleagues and I will not be bullied or intimidated."
SDLP leader Alasdair McDonnell said the bombers were reckless.
"The cowards, thugs and bullies behind this attack should be ashamed of themselves," he said.
"Whatever they think of the political process, they should channel their thoughts via the ballot box on May 22 and not by skulking around in the dead of night throwing petrol bombs."