The UVF has threatened to "orchestrate and participate in serious disorder" in east Belfast, police have said.
The threat follows a day of tension after contractors escorted by police officers cleared two bonfire sites.
A significant police presence remained in place in parts of east Belfast tonight.
Video: Cluan Place bonfire removed
Concerns had been raised over the safety of the pyres at Bloomfield Walkway and Cluan Place.
Yesterday, a High Court judge ordered that the Bloomfield Walkway bonfire be reduced in height.
Police moved into the area at around 5.30am this morning, but loyalists set it alight before the material could be seized.
The Cluan Place bonfire was eventually cleared.
Hundreds of bonfires are set to be lit at midnight as part of a loyalist tradition to mark the anniversary of the Battle of the Boyne in 1690.
The threat from the UVF is believed to be directed at police officers.
PSNI Assistant Chief Constable Alan Todd said as a result of the threat, he is reviewing his resourcing plans.
"Police have received information from the community which indicates that the east Belfast UVF intend to orchestrate and participate in serious disorder in east Belfast this evening directed against my officers," he said.
"I would strongly urge people to desist from engaging in any violent or criminal behaviour.
"I would also appeal to those who have influence in this community to discourage people from taking part in any illegal activity.
"The safety of the public and my officers is of paramount importance and accordingly I will be reviewing my resourcing plans to ensure there is an appropriate and proportionate policing operation in place to deal with any disorder should it occur."
The PSNI has also confirmed that a viable pipe bomb has been found at a peace line in east Belfast.
It follows reports of a loud bang at the barrier close to the Cluan Place area this afternoon, where earlier a bonfire was removed by contractors under police protection.
The remains of the device were found on the nationalist side of the peaceline on Clandeboye Drive.
A PSNI spokesman said: "The remnants of what is believed to be a viable pipe bomb type device have been found in Clandeboye Drive and we would ask for your patience and support as police work to make the area safe."
In Newtownards, Co Down a bus carrying passengers was hijacked by masked men, who were believed to have been carrying firearms.
None of the passengers were injured in the incident which took place around 7.30pm.
The bus was hijacked in Blenheim Drive and later set on fire.
Police were also at the scene of nearby Messines Road which was blocked by burning tyres.
And there were reports of a security alert in the area of Belfast City Airport tonight as Sydenham Bypass was closed and passengers were forced to remain in the terminal.
Belfast City Airport tweeted at 9.40pm that the airport has reopened and is now fully operational again.
