Arlene Foster claims Sinn Féin have 'surrendered power'
DUP leader Arlene Foster has claimed Sinn Féin are 'boycotting' the assembly and executive, amounting to a "surrender of power".
The former first minister said the continued impasse at Stormont "cannot be allowed to continue".
She spoke out after the Court of Appeal dismissed a bid by the Department for Infrastructure to have a High Court judgment over a waste incinerator overturned.
In May, a High Court judge ruled that a senior civil servant did not have the power to grant planning permission for a £240 million waste treatment centre and incinerator at Hightown Quarry in Mallusk.
The decision had been made by the permanent secretary of the Department for Infrastructure in the absence of a minister.
The north has had no executive for 18 months since the fall of Stormont.
Mrs Foster said the judgment "brings a sharp focus" on the absence of ministers in Northern Ireland.
"It is not acceptable and cannot be allowed to continue," she said.
"Key public services such as schools, hospitals and roads are being unfairly impacted."
She called on Sinn Féin to reach agreement with her party to restore devolution.
"Four out of the five main parties would form an executive today," she said.
"In the absence of an executive, decisions must be made in London.
"Last Friday, I welcomed the government's statement that it would 'take whatever steps necessary to provide good governance'.
"I told the Prime Minister on Monday that it is now time to follow those words with actions.
"I welcomed the commitment from the Prime Minister that she is exploring a number of options."
Mrs Foster claimed that Sinn Féin "collapsed the executive" 18 months ago and "have refused to re-enter the assembly since".
"This has created a back-log of decisions which require Ministerial sign-off. Civil servants cannot be left in this limbo.
"On the back of this judgement, we will again be pressing the Government to take decisions. Sinn Féin’s surrender of power and boycott of the House of Commons, Assembly and Executive cannot be allowed to cause further chaos in Northern Ireland.”
Sinn Féin has previously blamed the DUP for a failure to restore devolution.
The party's deputy leader Michelle O'Neill said in June that she believes devolution can be restored, but "only if there is political will there".
She insisted the reason for the failure "firmly falls at the feet of the DUP".