The government is trying to criminalise Sinn Fein through the International Monitoring Commission, Bairbre de Brun has said.
Bairbre de Brun addressed a Hunger Strike commemoration
Ms de Brun said the setting up of the body, which monitors paramilitary activity in Northern Ireland, was a breach of the Good Friday Agreement.
It threatened to further damage the credibility of the political process, she told a rally at Belfast City Hall to commemorate the 23rd anniversary of the Maze prison hunger strike on Sunday.
The International Monitoring Commission's first report highlighted the levels of paramilitary activity by republican and loyalist groups, and recommended financial sanctions on Sinn Fein and the Progressive Unionist Party.
Both parties have vowed to challenge the move.
Ms de Brun said Sinn Fein's commitment to the political process could not be questioned.
"It comes from our desire to see conflict ended and a new future built for everyone on this island, but we cannot do this alone.
"The British Government must fulfil its commitments and the Irish Government has a duty and an obligation as co-guarantors of the Agreement to stand up for the rights of Irish citizens living in the north.
"Tony Blair must learn the lessons of the past, end his policy of criminalisation and live up to his commitments under the Good Friday Agreement."
The latest crisis in the political process was triggered by the alleged false imprisonment of dissident republican Bobby Tohill in February.
Within hours of the incident, Chief Constable Hugh Orde said the IRA was behind it.
It led to Ulster Unionist leader David Trimble withdrawing from the review over Sinn Fein's continuing participation in the talks.
Devolution was suspended in the province in October 2002 amid allegations of IRA intelligence gathering at Stormont.