Catholics and Protestants accused each other Tuesday of provoking a riot in Belfast's polarized north side in which 25 police officers and an unknown number of civilians were injured.

Several hundred Catholic men and youths attacked British troops and police Monday night immediately after a small parade by the Orange Order (search), Northern Ireland's major Protestant brotherhood, had passed by under heavy security.

The violence overshadowed a largely peaceful day of mass protests by Orangemen on Northern Ireland's most divisive holiday, "The Twelfth," which commemorates the 1690 Battle of the Boyne (search), where the newly installed Protestant King William of Orange defeated the deposed Catholic king of Britain and Ireland, James II.

It also underscored how divided parts of this British territory remain despite the past decade of peacemaking efforts and the partial success of a 1998 peace accord.

In Dublin, Irish Prime Minister Bertie Ahern (search) called the rioting "deeply regrettable and disturbing," particularly because "considerable efforts had been made in the run-up to the march to defuse tensions in the area and to try and avoid such trouble."

Nonetheless, Ahern — whose government works closely with Britain in managing Northern Ireland's peace process — said the Orangemen's mass demonstrations had triggered no trouble in several other chronic flashpoints.

"It is important that we build on this in our efforts to ensure that the rest of the summer remains calm and peaceful," he said.

Catholics insisted that police should have blocked other Protestants from following about 200 Orangemen on the main road past the Ardoyne (search), one of the most hard-line Catholic districts in Belfast.

When police allowed a crowd of about 400 Protestants through separately, the Catholic crowd immediately began throwing bottles, rocks and even golf balls over police lines into the Protestant crowd, which picked up and threw back many of the objects.

Once the Protestants had passed through, the Catholic crowd then turned its rage on British troops starting to withdraw from the area. Young men used hammers to smash the windows of armored jeeps while others jumped on their roofs, rocking them in a bid to tip them over.

Rioters also snatched soldiers' clubs and shields, triggering charges by riot police and, eventually, the use of a massive mobile water cannon to quell the crowd.

Catholic hostility to the Protestants' traditional marches continued to flare Tuesday. Youths threw gasoline bombs at a train carrying Protestants to a parade in Lurgan, 30 miles southwest of Belfast, but caused no injuries.

Mark Durkan, leader of a political party that represents moderate Catholic opinion, met the British governor, Northern Ireland Secretary Paul Murphy, to discuss his community's anger over how the Orange parade past the Ardoyne was handled.

A government-appointed Parades Commission has been issuing restrictions since 1998 on Protestant parades that pass near or through Catholic areas. Last week it ruled that the Orangemen's parade past Ardoyne — recognized by all sides as the most likely spark for a riot this year — should not include any supporters or accompanying bands of fife and drum.

The Orange Order threatened to stage a mass protest of thousands of members unless the supporters, many of them drunk and verbally aggressive, were allowed to walk.

After hours of negotiations, the police decided to require the bands to speed past Ardoyne in three buses, while the supporters walked through several minutes behind the Orangemen — a compromise that both sides condemned from opposite points of view.

Durkan accused police commanders of "exploiting a technicality that went against the logic of the Parades Commission determination."

But Nigel Dodds, a hard-line Protestant politician and Orangeman who represents North Belfast in the British Parliament, said the Parades Commission (search) had no authority to place restrictions on ordinary civilians who were not part of marching organizations. He noted that a Belfast judge had confirmed this in a ruling last Friday, obliging the police to make different plans.

Dodds said the commission's "inept handling — purporting to ban supporters when a legal challenge showed it had no jurisdiction to do so — added immensely to the difficulties faced by people on the ground working to achieve peace and quiet."