Streets in the Donegall Pass area were blocked as hijacked vehicles, including a van, were set on fire.

Up to 30 masked youths, some armed with catapults and axes, bombarded police with petrol bombs and stones.

One officer sustained burns to his face as the vehicle he was in was petrol bombed. He is being treated in hospital.

Crates of petrol bombs

A police spokesman said one plastic bullet was fired by the security forces.

Police sealed off a large area between the Ormeau Road and the city centre at Shaftsbury Square as more cars were set alight..

A restaurant had to evacuated as the violence continued.

Police arrested a 36-year-old man for riotous behaviour and a 39-year-old man for disorderly behaviour in connection with the disturbances.

The latest trouble follows an outbreak of violence in the same area early on Sunday morning.

The trouble began at about 0200 BST when bottles and other missiles were thrown in the Donegall Pass area of the Ormeau Road.

Two people were injured and there were a number of arrests.

Police later seized two crates of petrol bombs at Walnut Street in Donegall Pass.

There is obviously also still activity, orchestration of violence by the paramilitaries on all sides, and that is very worrying

John Reid Secretary of state

South Belfast Ulster Unionist Michael McGimpsey accused republicans of provoking trouble in the area.

Mr McGimpsey said republicans were intent on creating trouble to coincide with the marching season.

In east Belfast, soldiers have begun work on raising the height of the interface wall between the Protestant Cluan Place area of the Albertbridge road, and the Catholic Clandeboye Drive area in Short Strand.

The Army said the wall - currently up to 4m high - will be increased by up to a further 3.5m.

The Army hopes to complete work on two sections of the wall by Sunday night, but said the entire project could take several weeks to complete.

'Saddened'

Speaking on the BBC's Breakfast with Frost programme, Secretary of State John Reid said there was obvious paramilitary involvement in the recent violence.

"This is not a new thing. What I think is more worrying is the general lack of confidence that we are now getting in the process.

"Enormous efforts have been spent in moving the peace process forward.

"There have been enormous benefits. There is obviously also still activity, orchestration of violence by the paramilitaries on all sides, and that is very worrying."

Entire project could take several weeks to complete

Meanwhile, the Church of Ireland Bishop of Down and Dromore, the Right Reverend Harold Miller, has sent a message to parishioners in east Belfast.

He said he was deeply saddened by the violence.

He said it seemed to be in the interest of cynical paramilitary groups to keep the conflict going.

On Saturday, a Catholic school in east Belfast was damaged in an arson attack.

Fires were started and flammable liquid poured into an art room and corridor at Our Lady and St Patrick's College in Kingsway.

A petrol bomb was also thrown into the building during the attack.

There were also attacks on houses in Belfast and County Antrim.