Michelle O'Neill says the government must call time on its discussion with the DUP to restore Stormont.
Speaking at her party's annual party conference, the Sinn Féin Vice President told reporters: "I think the British government needs to call time on the negotiations with the DUP because they are letting this drift endlessly over 18 months past the election.
"I just don't think that's a tenable position.
"The British government is pandering to the DUP and they need to call time on that as of now.
"I think public patience is completely wearing thin.
"There's no doubt everyone thinks the DUP needs to end its boycott and go back into the Assembly and take on the issues of the day," she added.
Stormont's First Minister in waiting was asked if the British-Irish Council and the British-Irish Intergovernmental Conference, which are due to take place at the end of November, would offer a good opportunity for the two governments to begin discussing a Plan B if devolution is not restored soon.
Ms O'Neill replied that that conversation should be happening now.
"Obviously we are still focused on Plan A.
"We want to get into the Executive, but equally it's prudent to plan for what comes in the aftermath if that is not the case and the British-Irish Intergovernmental Conference is a good juncture for that conversation to be had."
The Party's Ard Fheis is being held in Athlone.
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