British spies may have orchestrated the abusive messages sent to JK Rowling after she spoke out against independence, a leading SNP politician has claimed.
Christina McKelvie said the torrent of online attacks aimed at the Harry Potter author could have been the work of "secret service plants".
Ms McKelvie discussed MI5 involvement while saying there was no link between the vicious messages and the campaign fighting for Scottish independence.
The bizarre intervention follows outcry over the online reaction Rowling recently received after donating £1 million to Better Together, the pro-UK campaign.
The writer was variously described as a "traitor," "whore" and "specky b******" by internet nationalists – so-called cybernats – who were furious at her public support for the Union.
One Edinburgh-based charity was investigated by regulators after calling Rowling a "b****" in a tweet while Police Scotland reportedly examined an allegation of "online criminality" against the author.
Writing in her local paper, the Hamilton Advertiser, Ms McKelvie discussed Twitter and the "rather obsessive journalists" who watch the social media site.
"The attacks on JK Rowling for her donation to Better Together were, in fact, down to a very few people whose accounts no one could trace back to having anything to do with the Yes campaign," said Ms McKelvie, who chairs Holyrood's European and External Relations Committee.
"Whoever made them – there are interesting conspiracy theorists who think it might all have been down to secret service plants – should be totally condemned. I have no time for this kind of small-minded viciousness."
Earlier this month Jim Sillars, former SNP deputy leader, also suggested British spies may be actively working against the independence campaign.
"Are you unaware of the role agent provocateurs, special branch and MI5 have played in undermining us?" Mr Sillars wrote in an open letter to cybernats.
"Are you so naive, that you never think that perhaps MI5 and special branch are taking a role in this campaign? As their function is protection of the British State, they would not be doing their jobs if they were not."
A Number 10 source dismissed Ms McKelvie's claims as "preposterous and extraordinary" while Michael McMahon, a Labour MSP, said the remark "would be laughable if it wasn't so serious".
"The nationalists are really starting to lose touch with reality. First Jim Sillars said MI5 was out to get them, now Christina McKelvie blames the Secret Service for the awful abuse directed at JK Rowling by nationalists," Mr McMahon said.
"Instead of coming up with ludicrous conspiracy stories, the nationalists should start giving Scots answers about what would replace the Pound or how pensions would be funded if we leave the UK.
Rowling was not the first person to be sent abusive messages after speaking out for the UK before the Scottish independence referendum on September 18.
David Bowie was told to "f*** off back to Mars" after urging Scotland to "stay with us" during a speech at the Brit Awards.
Sir Chris Hoy, six-time Olympic gold medallist, was called a "bigoted anti-Scot" after pointing out most Scottish athletes rely on facilities in the rest of the UK.
Susan Calman, a Scottish comedian, received internet abuse and death threats after joking about the independence referendum on a radio show.
High profile figures from both sides in the campaign have received abusive messages online. Last weekend it emerged that police are looking into a death threats made about Mr Salmond on Facebook.
One post reportedly said there was a plan to "hire a hitman" to kill the First Minister, while another said "someone needs to take him out". Leaders from both sides of the debate have condemned all forms of abuse.