The Scottish Government has not clearly established the cost of implementing newly devolved powers, a spending watchdog has warned.

A new report from auditor general Caroline Gardner examines the progress towards putting new powers devolved under the 2012 and 2016 Scotland Acts into practice.

It warns the government has not estimated the total cost of implementation or the extent to which it will exceed the UK Government's £200m contribution.

Any excess costs will have to be paid by the Scottish Government.

Ms Gardner has called for improved transparency, urging ministers to develop and refine more detailed estimates of how much it will cost to implement the powers.

The report identifies good early progress on Scotland's new social security programme but says it is at a "critical" point in the run-up to the planned delivery of the first wave of devolved benefits by summer 2019.

"A significant amount of work is required during 2018 if planned timescales are to be met," it states.

Ms Gardner also warns it will be "challenging" for the government to recruit and deploy the necessary skilled staff in time.

She said: "Putting the Scottish Parliament's new financial powers and social security responsibilities into action is a huge and highly complex piece of work.

"More detailed workforce analysis and a much more transparent picture around overall costs are needed to ensure the right people and infrastructure are in place in time.

"Good early progress has been made on the government's social security plans but they are now at a critical point."

A Scottish Government spokesman said it "fully recognises" the need for transparency over the costs of the scheme.

"We will provide information in our own progress report to Parliament on implementing the Scotland Acts and we are putting comprehensive Scottish Exchequer governance and assurance arrangements in place," he said.

"Suggestions that we have not estimated implementation costs do not recognise that these costs are only one element of a large and complex Scottish budget.

"All spending pressures, whether from implementation of the Scotland Acts or any other commitment, are considered when setting budgets."