Nicola Sturgeon has accused the UK Government of leaving her government and the other devolved administrations "substantially in the dark" on key Brexit talks.
The First Minister hit out on the issue ahead of a meeting of the British Irish Council, which brings together representatives of all the governments on the British Isles.
Ms Sturgeon will attend the summit in Jersey with Scottish Brexit minster Mike Russell and External Affairs Secretary Fiona Hyslop.
Ahead of the meeting she called on the UK Government to make good on its promise to give the devolved administrations a "genuine role" in discussions about exiting the European Union (EU) , claiming they had instead been "cut out" of the talks.
Ms Sturgeon said: "In less than 18 months' time, the UK will be leaving the EU but despite reassurances that all devolved administrations will be consulted on the withdrawal negotiations, we remain substantially in the dark.
"The UK Government assured us that the Joint Ministerial Committee (JMC) would seek to agree UK positions and discuss issues stemming from the negotiations, respecting the devolved competencies, but the UK Government then allowed that process to fall short of what is required,"
There has only been one meeting of the JMC on EU negotiations since talks began on June 19, Ms Sturgeon said.
She insisted: "This is not an abstract debate about process. Leaving the EU will have an enormous impact on Scottish jobs, our economy and our relationship with the world - indeed, Brexit's effects are already being felt.
"We know from businesses in Scotland that a hard Brexit will cause serious and long-term economic damage, and it is crucial we stay in the single market and customs union."
The First Minister said: "As has previously been said, the clock is ticking on Brexit and it is essential that the UK Government live up to its promises to give devolved administrations a genuine role on what is by far the most important issue facing every corner of these islands."
The talks are also taking place at the same time as tax arrangements in the Channel Islands have come under scrutiny in the wake of the leaked Paradise Papers, with the Jersey government having announced it will be investigating some of the allegations.
A UK Government spokesman said: "These comments come just weeks after an agreement was made at a Joint Ministerial Committee between the UK Government and the devolved administrations, including the Scottish Government, on the principles that will underpin the process for bringing back powers from the EU to the UK.
"There has been an unprecedented level of engagement between ministers and officials in devolved administrations which will continue. We are committed to securing a deal that works for the entire UK including Scotland."