First Minister Nicola Sturgeon has rejected a claim that the head of the Scottish National Investment Bank (SNIB) resigned in relation to a new economic strategy.

Chief executive Eilidh Mactaggart announced she was stepping down from the SNIB last Friday – something Ms Sturgeon said ministers had been notified of earlier in February.

But Conservative leader Douglas Ross claimed the timing was “suspicious”, with the National Strategy for Economy Transformation being announced on Tuesday.

Ms Sturgeon refused to address the reasons for Ms Mactaggart’s resignation, which comes 18 months after her appointment, citing her right to privacy.

“Everyone across the chamber will understand that I’m not going to go into the confidential details of anybody’s employment situation here in the chamber,” she said during First Minister’s Questions.

“This issue is not a matter for Scottish Government ministers, it’s a matter for the board of the Scottish National Investment Bank – ministers had no input into that, although we were told earlier in February that the chief executive would be leaving the bank imminently.”

Ms Sturgeon added it is for the Scottish Government to ensure that the “bank was performing well”.

She added: “And the bank is performing exceptionally well.”

Mr Ross responded: “The First Minister has used this opportunity to explain how well the bank is doing and the vital work they are undertaking and therefore I think it is important that this Parliament knows and the public in Scotland know why the chief executive resigned so abruptly earlier this week.”

He questioned the parallels between the release of the economic plan and Ms Mactaggart’s decision.

“The timing about this is all very suspicious,” he claimed.

He said the chief executive had resigned “just days before the SNP launched their own economic strategy – a strategy that is wafer thin, underwhelming and watered down by the Greens”.

The strategy, at the launch of which the Finance Secretary pledged Scotland would be “radical and bold”, received a mixed response when it was published on Tuesday.

Several business groups, including the Scottish Retail Consortium and the Scottish Chambers of Commerce, welcomed it, while businessman Sir Tom Hunter called for the plan to be more business-led and STUC general secretary Roz Foyer – who was a member of the group which advised government on the plan – said it was a “missed opportunity”.

Ms Sturgeon added: “Yes, it is a coincidence and that is clear.

“On the issue of the former chief executive – the former chief executive of the Scottish National Investment Bank is a private individual.

“She has opted to resign her post as chief executive of the bank – she is entitled to the duty of care and the confidentiality that any other individual in her circumstance is entitled to.

“It would be completely wrong – and I think most reasonable people would accept – that it would be completely wrong of me in the chamber of the Scottish Parliament to breach that confidentiality.”

After First Minister’s Questions, Liberal Democrat MSP Willie Rennie said that if Ms Mactaggart is leaving due to personal reasons, MSPs should be told so.

“If the reason for resignation was personal I think everyone would respect that and saying so would end this debate, but if it is related to the function, policy or delivery at the bank then we have a right to know – especially as considerable public sums are at stake,” he said.