Belfast, Northern Ireland (CNN) -- Authorities accused pro-British extremists of exploiting protests in Northern Ireland over the Belfast City Council decision to stop a century-old tradition of flying the Union Jack year-round.
The protests calling for the council to reverse its ruling over the flag continued Monday evening, police said. About 400 people gathered at Belfast City Hall as the City Council met for the first time since it voted to fly the British flag only on certain days, police said. The protest, which was mostly peaceful, was organized via social media, authorities said.
In East Belfast, about 250 protestors gathered, and missiles such as petrol and paint bombs, fireworks and heavy masonry were thrown at police. Police responded with water cannon, authorities said, and overall calm had been restored Monday night.
Four people, two males and two females, were arrested, accused of riot and public order violations, police said.
Authorities say at least 52 officers have been wounded in protests.
The chief constable for the Police Service of Northern Island put the blame for the violence on members of the loyalist Ulster Volunteer Force, who were "orchestrating violence for their own selfish motives."
The British flag, the Union Jack, has long been a flashpoint between British loyalists -- primarily Protestants -- who want to remain part of the United Kingdom and Irish nationalists calling for Northern Ireland to join Ireland.
Northern Ireland's political leaders have called for an end to the pro-British protests, and politicians, clergy and community met Sunday to discuss possible ways to bring about an end to the unrest.
"Everyone involved needs to step back. The lack of control is very worrying," Chief Constable Matt Baggott told CNN.
"The only answer is a political solution."
A large number of police officers have been pulled away from their normal duties to deal with the demonstrations, Baggott said.
If this continues, "it will eat into our ability to deal with drugs, into our ability to deal with alcohol issues, and deal with what is a very severe dissident threat."
Among the more than 70 arrested since the protests began was a 38-year-old man who was arrested Saturday on suspicion of attempted murder and being in possession of a gun. Police said that at the time of the man's arrest, there were reports of shots being fired at police.
The vote on the flag followed a summer of heightened tensions between Northern Ireland's Catholic and Protestant communities. Riots in September left dozens of police officers injured.
The majority of the island gained independence in 1921, following two years of conflict. But six of the nine counties of the province of Ulster chose to stay in the United Kingdom, eventually becoming the country of Northern Ireland.
In the late 1960s, the conflict between mainly Protestant loyalists, who want Northern Ireland to remain part of the United Kingdom, and largely Roman Catholic nationalists, who want it to be reunited with the rest of Ireland, exploded into a political and sectarian war, known as "the Troubles."
The three decades of ensuing violence between loyalists and the IRA claimed more than 3,000 lives, most of them north of the border. While the Good Friday Agreement of 1998, also known as the Belfast Agreement, effectively ended the conflict, distrust remains between Catholics and Protestants.
Under the terms of the accord, groups on both sides dumped their weapons, and members of Sinn Fein, the political affiliate of the IRA, now work with pro-British politicians in Northern Ireland's power-sharing government.
CNN's Chelsea J. Carter contributed to this report.