The Prime Minister has urged the leader of the Democratic Unionist Party (DUP) and Sinn Féin’s northern leader to reach a deal to restore power-sharing.
Theresa May spoke to the DUP’s Arlene Foster and Sinn Féin’s Michelle O’Neill in separate phone calls on Friday.
Mrs May said it was “encouraging to see discussions continuing”, No 10 said.
However, Sinn Féin president Gerry Adams said he did not expect a deal to restore Stormont power-sharing to be struck by Monday.
The talks finished on Saturday afternoon and are expected to resume on Monday.
However, the mood so far has not been positive ahead of a statement by the secretary of state on Monday.
James Brokenshire has the option of extending the talks, calling another assembly election or reintroducing direct rule.
On Saturday, he said: “I still believe power-sharing can happen, but it has not happened yet.”
Mr Brokenshire said there were no deadlines but he would be making a statement to Parliament on Monday afternoon to update the House of Commons on what the next steps in the talks might look like.
Earlier, Mr Brokenshire had said that the absence of devolved government in Northern Ireland “cannot continue for much longer”.
He said the Northern Ireland Civil Service “has effectively been running the show” and decisions on budgets need to be taken by politicians.
The BBC understands Friday talks ended at about 19:30 BST, breaking up fairly abruptly and not in a positive mood.
The Prime Minister told the DUP leader that the government was committed to “doing everything we can to work with the parties to reach a successful conclusion”.
A No 10 spokesperson said Mrs Foster and Mrs O’Neill “both agreed on the need for the Executive to be restored for the benefit of everyone in Northern Ireland”.
The Prime Minister recognised that constructive discussions had taken place between the parties and urged them both to come together to “reach a collective agreement so that devolved government could be restored in Northern Ireland.”
Meanwhile, the independent chair of the talks to restore power-sharing in Northern Ireland has agreed to remain at the helm after his retirement on Friday.
Sir Malcolm McKibbin has formally stood down from his role as the head of the civil service in Northern Ireland.
But the parties have asked him to continue chairing the negotiations to steer them through the weekend.
The DUP and Sinn Féin remained deadlocked on several issues.
Sinn Féin’s demand for an Irish language act is a major stumbling block, with the DUP refusing to agree to it as part of any deal.
On Friday, Sinn Féin called on the UK and Irish prime ministers to enter the talks
The DUP’s Edwin Poots hit back by saying the republican party “don’t need anyone to hold their hands”.
The DUP will not be present for discussions on Sunday.