Sinn Féin's vice-president Michelle O'Neill has launched a strong attack on the DUP, claiming the party is "living in a fool's paradise."
Mrs O'Neill was making her first speech to an ard fheis (conference) since taking up the role.
She said the DUP puts its "self-serving pact with the Tory party at Westminster before people's interests here".
She added "they blindly prop up Theresa May who is preoccupied with negotiating with her cabinet rather than the EU".
The DUP and Conservatives agreed a "supply and confidence" arrangement following the general election in June last year.
Speaking on Friday night, Mrs O'Neill said: "Britain is divided. But in Ireland we are united.
"We will not be collateral damage as a result of the reckless Tory/DUP Brexit agenda. There will be no hard border in Ireland."
As part of the DUP/Tory deal, the DUP guarantees that its 10 MPs will vote with the government on the Queen's Speech, the Budget, and legislation relating to Brexit and national security.
The deal included an extra £1bn in public spending for Northern Ireland.