BELFAST (Reuters) - Fifty-six police officers and two civilians were injured in protests in central Belfast, the authorities said on Saturday, following the latest flare-up in violence stoked by tensions between Northern Ireland's Protestant and Catholic communities.

Many of the injuries were minor, but four officers were taken to hospital after the clashes late on Friday, during which the police fired plastic bullets and water cannon after being pelted with missiles for a second successive night.

Belfast remains divided between pro-British Protestants and Catholics who generally favour unification with Ireland, despite a 1998 peace and power-sharing deal that put an end to the worst of the so-called "troubles" in the British province.

"Last night's violence and attacks on police officers were shameful," Britain's Minister for Northern Ireland Theresa Villiers said in a statement.

"Disorder on the streets is a hugely regrettable step backwards."

Protestants had opposed a march on Friday evening along the city's main thoroughfare - Royal Avenue - by the nationalist side of the community, and when the police moved in to clear them, they threw bricks, bottles and fireworks.

Burnt-out cars and rubble littered central Belfast and shop fronts were damaged, as the cleanup work began on Saturday.

The Catholic parade, marking the anniversary of the 1971 introduction of internment without trial by the British authorities, eventually had to pass along a different route.

Forty-two years ago, soldiers swept into Catholic districts and arrested more than 340 people as the British government sought to halt growing Irish Republican Army violence aimed at extinguishing rule from London.

In all, more than 3,600 people died in a sectarian conflict that began in the late 1960s, including more than 1,000 members of the British security forces. More than 36,000 were injured.