Hundreds of men - all dressed in white shirts and black ties - lined an east Belfast street, sparking concerns.
The display of manpower coincided with a loyalist band parade on Saturday, and police have said they will review evidence gathered at the event.
The similarly dressed men flanked the parade as it made its way up Newtownards Road. Images and videos shared on social media show the line stretching a few hundred metres from Dee Street to Holywood Arches.
Banners reading ‘Vol Robert ‘Squeak’ Seymour Memorial Parade’ and others supporting the UVF had been put on display in parts of the district in recent days.
UVF member Seymour was shot dead by the IRA in 1988.
SDLP councillor Séamas de Faoite said it is “disturbing” that 26 years after the Good Friday Agreement “we’re still witnessing pantomime like this on the streets”.
“People in east Belfast want to see action on the housing crisis, long-standing deprivation and poverty and the failure of political leadership to deliver,” he said.
“They don’t want to see these throwbacks to the past.
“Its time for all of those involved in criminality and mafiaesque behaviour to get off the backs of the people of East Belfast.
“Their day is done.”
It is understood police are aware the presence of the men at the parade is being linked to ongoing tensions within the UVF.
A PSNI spokesperson said a “policing operation” was in place for the “notified procession organised by the 36th (Ulster) Division Memorial Association”.
“At the procession’s height, it is estimated that as many as 1,500 people in plain black trousers, white shirts and ties lined the route,” they said.
“The procession passed off without incident. A further review of evidence gathered will now take place.”
Tensions within the UVF have been simmering since last year when the group’s leadership in east Belfast, including its alleged former commander Stephen ‘Mackers’ Matthews, were stood down.
The decision to remove several senior command figures is believed to have been taken by the UVF’s Shankill Road-based leadership.
Matthews denies any link to either criminality or the UVF.
The organisation in east Belfast has been linked to the drugs trade and other criminality in recent years and it is regularly targeted by the Paramilitary Crime Task Force.
Hostilities between rival factions surfaced earlier this year ahead of a commemoration for two UVF men killed in a premature bomb explosion almost 50 years ago.
Tensions continued to rise when UVF posters warning against drug dealing appeared in east Belfast in March.
The posters, headed with the words ‘Ulster Volunteer Force’ and including the paramilitary group’s distinctive crest, also urged those who owe money to criminals not to pay it back.
They included the words “do not lend money” and urged anyone with information about drug dealing to report it to their local political representatives.
A similar poster put up in the Newtownards Road area carried the warning “do not lend money”.
Graffiti also appeared in east Belfast bearing the words ‘East Belfast UVF’ and ‘F**k the Shankill’.
It was later painted over.
