Police are investigating a complaint that controversial BNP leader Nick Griffin was responsible for “inciting hatred” after making a foul-mouthed sectarian remark about Catholics.
The far-right MEP described republicans as “fenian bastards" on Twitter, hours after a surprise appearance at Stormont.
A formal complaint was lodged with the PSNI by Belfast SDLP councillor Nichola Mallon on Sunday.
“His presence at Stormont was deeply unhelpful and should have been challenged. All Nick Griffin seeks to do is stir up discontent and sectarianism in Northern Ireland, and that is the last thing we need,” she said.
A PSNI spokeswoman confirmed: “Police have received a complaint regarding the matter and are investigating.”
Griffin, however, defending using the insulting term, said: “It wasn't about Catholics, it was about the operatives of the republican grievance exploitation machine who were leaving foul-mouthed tweets on my Twitter feed.
“It was about them specifically. They're the ones I had a go at.”
Griffin was spotted handing out leaflets at Stormont. He later posted a series of photographs of the event on his Twitter account.
In one message, he referred to Lambeg drums, adding that they were “banned in some places to appease Republican bigots”.
When challenged by followers, Griffin was defiant. “So Ulster pics have upset my Republican stalkers. Tell you what, the bodran can't match the lambeg, you fenian bastards,” he wrote.
DUP councillor and Orangeman Christopher Stalford said: “One knuckle-dragging MEP turning up does not mar the whole day. I just think it's sad that it has received the attention it has.”