Time is running out for a breakthrough to be found in the constitutional impasse between Holyrood and Westminster over a post Brexit "power grab", a spokesman for Nicola Sturgeon has said.
It comes amid reports that a compromise offer from UK ministers was rejected by the SNP on the transfer of powers back from Brussels over concerns it still undermines the devolution settlement.
The Scottish Government's Europe minister Mike Russell will meet with UK ministers this week in an effort to broker a deal.
Read more: Holyrood Brexit power grab fears ‘could harm future of UK’
But a spokesman for Nicola Sturgeon warned to that "time is of the essence."
He added: "We're still talking, we're still intent on being as co-operative as possible, but obviously time is running short and we haven't had the progress so far that we need to see."
Although no firm cut off deadlines have been set, an agreement will need to be reached well in advance of the UK's departure form the EU in March next year. The concerns centre on the EU Withdrawal Bill which will return Powers residing with Europe to the UK after Brexit.
Read more: Scotland facing constitutional crisis over Brexit bill
The UK Government has reportedly offered to devolve about 100 powers to Scotland in an effort to break the deadlock with the SNP in Scotland over claims of a "power grab."
But it was claimed that UK ministers would retain a veto over certain areas to ensure common "UK frameworks" apply and Ms Sturgeon's spokesman made it clear this would be unacceptable.
"We've made clear consistently that we're intent on protecting the existing devolution settlement and we're not prepared to sign up to a deal that jeopardises or cuts across the existing devolution settlement," Ms Sturgeon's spokesman added.
The Scottish Government is not opposed to some frameworks in areas such as packaging of goods, to ensure the smooth running of the UK internal market, the spokesman said.
But he said: "That cannot be by imposition - frameworks would have to be agreed by mutual consent. If you're talking about an offer which involves in some way constraining the power of the Scottish Parliament in areas which are already devolved, then clearly that impinges on the existing devolution settlement and that's unacceptable."
Many of the EU powers returning to the UK in areas such as farming and fishing belong at Holyrood, according to the Scotland Act that brought about devolution. But the bill drawn up at Westminster proposes that these will all be transferred to Westminster at the point of Brexit, before UK ministers decide which additional responsibilities are then to be passed onto Holyrood. This has been branded a power grab by the SNP ministers.