23 police officers and an MP were among those injured during a night of fierce violence in Northern Ireland.
Twenty-nine police officers were injured during sectarian riots between republicans and loyalists in east Belfast today.
The union flag will be raised at dawn over Belfast City Hall for the first time since the dispute began last month.
Police have deployed water cannon and fired plastic baton rounds in a bid to quell the trouble.
Two police officers have been injured in the initial clashes with loyalists ahead of a republican parade, the Police Service of Northern Ireland (PSNI) confirmed.
Both have been taken to hospital for treatment, a PSNI spokeswoman said.
Police have come under attack from loyalists in Belfast city centre ahead of a republican parade.
There were clashes in the Royal Avenue area, with officers pelted with bricks and other missiles, as hundreds of loyalist demonstrators gathered to protest at the rally to mark the introduction of internment in Northern Ireland during the Troubles.
Protesters have attempted to block part of the route the Anti-Internment League parade is due to take later this evening.
Police have advised the public to avoid the area.
Eight police officers have been injured following a night of serious disorder at an anti-internment bonfire in west Belfast.
Paint bombs, bottles and other items were thrown at police in the Divis area overnight. The Lord Mayor of Belfast, Sinn Fein's Máirtín Ó Muilleoir condemned the violence.
Disorder also flared in North Belfast, where a man attacked police with a sword. Police are also investigating reports that a stolen loyalist artwork has been placed on top of the bonfire. In a statement, the PSNI said:
A thorough investigation is now underway to identify all those involved in the disorder.
Later thousands are expected to take part in a march through the city centre to commemorate internment, which began on August 9 1971 when the army arrested 342 people suspected of being in the IRA and held them without trial.
A total of 1,981 men and women were interned while the policy lasted.
Belfast's Lord Mayor, Sinn Fein's Mairtin O'Muilleor, has been attacked by loyalist protesters at the re-opening of a children's park in north Belfast.
Mr O Muilleoir, 53, required a police escort to evade angry protesters at the re-opening of a park in the staunchly unionist Woodvale area.
The high-profile businessman and city councillor said he was kicked and punched during the altercation. Police said nine of their officers were injured during the incident, although none required hospital treatment.
Community tensions are high in Woodvale after recent loyalist rioting over a decision to prevent three protestant Orange Order lodges parading past the nearby nationalist Ardoyne area.
Loyalists have accused Sinn Fein of waging a cultural war against their community.
Watch UTV's video of the incident: Police shield SF mayor from protesters
In a statement released tonight the PSNI claimed the blast bombs were thrown by masked men in the Lower Newtownards Road area.
"The blast bombs thrown in the east Belfast area earlier this evening were thrown by masked men from the area of Pitt Park at police lines on the Lower Newtownards Road," a spokesman said.
Disorder has again erupted avross East and North Belfast with police coming under attack with petrol bombs and other missiles.
Up to four (psni) officers injured.
Democratic Unionist Party MLA for North Belfast William Humphrey described the pipe bomb attack as an attempt to kill.
– Democratic Unionist Party MLA for North Belfast William Humphrey
This nail bomb was not only a deliberate attempt to further inflame tensions in this area but was an attempt to cause death or serious injury. Fortunately despite this indiscriminate weapon exploding, no injuries were sustained.
Local people have already suffered enough as a result of the trouble within the area. There is absolutely no justification for violence from any quarter, and I would hope that this incident will be treated with the utmost seriousness.
Theresa Villiers, Secretary of State for Northern Ireland, also condemned the "deplorable attack" on police officers.
The Police Service of Northern Ireland has closed a number of roads in Belfast after bombs were thrown at officers in a fourth night of protests.
Due to large protest of several hundred people Twaddell Ave Nth Bt is currently blocked to traffic. Motorists advised to take avoid area
Police are currently dealing with public disorder in the Lower Newtownards Road area of East Belfast this evening.... http://t.co/iDM8DM3B0u
Crumlin Rd in North Belfast has been closed between Tennent St and Twaddell Ave. Motorists are advised to avoid the area.
An improvised explosive device was hurled from the nationalist Brompton Park area of Ardoyne and exploded after striking an armoured police vehicle just after 5pm.
There were no reports of any injuries.
Witness Sam Coulter, who was yards from the explosion at a loyalist protest, said it was fortunate no one was hurt.
– Witness Sam Coulter
We were standing having a peaceful protest when all of a sudden there was a bang and the next thing we heard the 'tinkle, tinkle, tinkle' of nails dropping on the ground.
I think it was directed at the protest - police were at the other side of the road behind a Land Rover. Luckily nobody was hurt - just a bit of a bang to the ears.The place is in lockdown now with police doing sweeps of the area to gather evidence.
This won't put us off our protest - we are still here.