The UK government is merely "going through the motions" in talks to restore powersharing at Stormont and is more focused on their efforts to strike a deal with the DUP at Westminster, Sinn Fein has claimed.
Conor Murphy said his party had serious concerns the deadline for saving devolution would be missed due the disengagement of both the DUP and Conservatives.
He rubbished any suggestion an agreement could be reached between the parties in Belfast before details of any Tory/DUP confidence and supply accord were published.
Mr Murphy said while the official deadline for a deal at Stormont was next Thursday - June 29 - the UK and Irish governments had told the participants an agreement had to be effectively reached by Tuesday.
"The reality is the British government are going through the motions here while their game is their own preservation of their own interests in London," he said.
The Sinn Fein negotiator added: "Thus far we have not seen, as the British government and the DUP have been distracted with other business, we haven't seen the level of engagement that is required here.
"We are seriously concerned given the time-frame we are operating here, given the lack of any visibility in terms of the deal being negotiated between the DUP and British government, time is fast running out on this process."
DUP Assembly member Simon Hamilton offered a contrasting view on the state of the talks inside Stormont Castle.
He said Thursday had been a "good day of engagement".
"We continue to make progress and we remain hopeful," he added.
He rejected the Sinn Fein claim that his party was distracted by events in London.
"The DUP is able to multi-task and represent the people of Northern Ireland both in London and here in Belfast," he said.
"We are putting our shoulder to the wheel to try to get a good deal in London and also get a good deal here in Belfast as well."
If the parties miss the deadline for agreement at Stormont they face the prospect of direct rule being reimposed from Westminster.
Northern Ireland has been without a powersharing Executive since March and without a first and deputy first minister since January, when the late Martin McGuinness's resignation forced DUP leader Arlene Foster from her job as first minister.
The institutions collapsed amid a bitter political row over a botched renewable heat scheme.
The anticipated DUP/Conservative arrangement at Westminster has forced the UK Government to reject suggestions its commitment to act with impartiality in Northern Ireland - as set out in the 1998 Good Friday Agreement - will be fatally undermined by any parliamentary pact.