The Police Service of Northern Ireland has warned that republican paramilitaries are planning major street violence in north Belfast today.
Assistant chief constable Mr Alan McQuillan said that Sinn Féin was planning to bus republican youths from across the North into Ardoyne for a protest against a controversial Orange Order march.
He also said that police had recovered several hundred empty bottles and paint and acid bombs during searches in north Belfast last night
Mr McQuillan said he believed republican paramilitaries were planning a major riot. He refused to say which paramilitary organisation was involved but police sources confirmed it was the Provisional IRA.
He said the aim of the perpetrators was to put the nationalist community into conflict with the police. He appealed to the Sinn Féin leadership to ensure "this madness" was avoided. "Nobody wants it," he added.
Last night shops, pubs, and restaurants closed early in Belfast, where many streets were deserted as the traditional eleventh-night bonfires began.
Sources on both sides of the political divide said they feared there could be serious disorder at feeder parades going to and returning from the main Twelfth demonstration past the Ardoyne and Springfield areas today.
Last year, there were serious clashes in Ardoyne involving nationalists, the police and loyalists as the Orangemen returned home.
Tensions have been running high in Ardoyne in recent days. A police CCTV camera close to the parade route was hit by high-velocity gunfire on Tuesday night. The INLA is believed to have been responsible.
The nationalist Springfield Residents' Action Group has withdrawn an application to protest at today's parade, leading to fears of a repeat of a fortnight ago when an unmarshalled group of 300 nationalists attacked the police after a mini-Twelfth parade passed by.
The group warned that there was "a very volatile and dangerous situation" in the area.
Spokeswoman Ms Frances McAuley said: "We are not prepared to facilitate, as we have done in previous years, the Orange Order's march through our area."
The North's Parades Commission last night rejected a last-minute appeal by Sinn Féin to review its decision on the two controversial Orange marches in the Springfield Road and Ardoyne areas.
In a statement, the commission urged all sides to show restraint. "The Parades Commission hopes that, over the next two days, those parading and their supporters show respect to their host communities and that those communities will demonstrate tolerance and respect of the traditions of the parades. It particularly calls on everyone to conduct themselves in a peaceful and lawful way."
Tens of thousands of Orangemen will celebrate the 312th anniversary of the Battle of the Boyne in parades today. The main demonstration will be held in Belfast.
The Sinn Féin Lord Mayor of Belfast, Mr Alex Maskey, yesterday met representatives from nationalist and unionist parties to urge them to use their influence to prevent trouble.
"I am aware that there is concern and worry out in our community and that there is perhaps a dangerous cocktail of circumstances out there. I am urging people to exercise political leadership by asking for calm and restraint."