Nicola Sturgeon told UK transport secretary Patrick McLoughlin that relatives of the 10 people who died when a police helicopter crashed on to the roof of the Glasgow pub on November 29 2013 are still waiting for answers.
An initial report from investigators said the aircraft suffered engine failure but the final conclusions of the Air Accidents Investigation Branch (AAIB) are yet to be published.
It said in November last year that the final report was expected to be published "in the middle of 2015".
In the letter, sent over the weekend, Ms Sturgeon said: "While I fully understand the need for the most rigorous possible investigation, taking account of all possible factors, I am concerned at this apparent slippage in timescale.
"The Clutha families have already waited for almost two years, and I believe they should have an assurance that the report is now nearing completion and will be published imminently and certainly before the second anniversary of the tragedy.
"I would be grateful if you could give urgent consideration to this matter and take any necessary steps to expedite the publication of the final AAIB report.
The First Minister has previously raised concerns about the speed of the investigation in a letter to the Prime Minister.
An AAIB spokesman said: "The Clutha investigation continues to ensure the AAIB is satisfied all evidence and any additional information has been fully considered.
"The report is now being reviewed and will be published in due course."
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules here