An Irish Republican Army mural on a building in Derry, Northern Ireland. Slogans celebrating the IRA, an anti-British paramilitary group, are common in predominantly Catholic and republican neighborhoods in Derry. (Photo by CAIN BURDEAU/Courthouse News Service)

(CN) — A riot against police broke out Thursday night in the Northern Irish city of Londonderry, long a center of sectarian conflict, and a 29-year-old journalist covering the unrest was shot to death, authorities said.

The riot broke out after police raided a housing estate known for its ties to dissidents affiliated with the New Irish Republican Army, a militant group seeking to push the United Kingdom out of Northern Ireland.

The violent events in Londonderry, a city also known as Derry, comes at a time of political turmoil in Northern Ireland, caused in part by the United Kingdom’s decision to leave the European Union. Brexit is believed to be fueling anti-British sentiment among dissident groups in Northern Ireland, who also call themselves republicans because they want all of Ireland to be a unified republic.

In the late 1960s, Northern Ireland was plunged into violence largely because of attacks against Roman Catholics in Derry, who were protesting their status as second-class citizens.

Scenes from Thursday’s riot were reminiscent of the Troubles, the decades-long conflict between pro-Irish and pro-British paramilitaries and their supporters. The conflict left more than 3,700 people dead.

Rioters threw more than 50 petrol bombs at police and their armored vehicles and set at least two hijacked vehicles on fire, according to Assistant Chief Constable Mark Hamilton of the Police Service of Northern Ireland.

Lyra McKee, a journalist, was shot and killed when guns were fired during clashes with police Thursday night in Londonderry, Northern Ireland. Police are investigating. (Family photo/PSNI via AP)

At about 11 p.m., a gunman shot at police and wounded journalist Lyra McKee, who later died at a hospital, Hamilton said.

“We believe this to be a terrorist act. We believe it’s been carried out by violent dissident republicans,” Hamilton said in a televised news conference Friday. “Our assessment at this time would be that the New IRA are most likely to be the ones behind this.”

He said a murder investigation has been opened.

“This is a horrendous act. It’s unnecessary, it’s uncalled for. It’s totally unjustified,” Hamilton said. “But not only is it a murder of a young woman, it’s an attack again upon the people of this city.”

McKee was a highly regarded Northern Irish freelance journalist and author known for her investigative work into the Troubles and their lingering effects on society. Her work has appeared in The Atlantic and BuzzFeed, among other publications. Her new book, “The Lost Boys,” is to be published next year and examines unsolved disappearances of children and young men during the Troubles.

The New IRA is blamed for a spate of actions this year. In January, the group allegedly planted a car bomb in front of a courthouse in Derry that exploded. The group then claimed responsibility for letter bombs sent to London and Glasgow in March.

In the days before Thursday’s unrest, tensions between police and dissidents in the Creggan housing estate were growing, according to news reports.

Dissidents were planning an unauthorized march on Monday to commemorate the 1916 Easter Rising, an armed insurrection against British rule in Ireland. Last year, the march featured masked men in paramilitary-style uniforms and police vehicles were attacked.

The Creggan neighborhood was the starting place of a civil rights march in 1972 that ended with the deaths of 13 civilians on what is known as Bloody Sunday.

On Friday, the parade organizers said they were canceling Monday’s march out of respect for the “tragic and accidental killing” of McKee, according to Derry-based reporter Leona O’Neill.

Police reportedly raided the Creggan estate to search for weapons and explosives stored by dissidents. Police believed dissidents were planning attacks, according to The Guardian newspaper.

Saoradh, a small radical political party that voices ideas similar to those of the New IRA, issued a statement condemning the police raid and blamed the journalist’s death on the raid.

“The blame for last night lies squarely at the feet of the British Crown Forces, who sought to grab headlines and engineered confrontation with the community,” the group said in a statement.

Saoradh called the police raid an “incursion” and part of “a campaign of oppression” against republicans in Derry. It said that republicans were victims of state violence and that police had been warned that actions in Creggan would “be met with resistance, as has historically been the case.”

Politicians expressed outrage.

British Prime Minister Theresa May called the killing “shocking and truly senseless.”

Ireland’s Prime Minister Leo Varadkar said, “We cannot allow those who want to propagate violence, fear and hate to drag us back to the past.”

Northern Ireland politicians also condemned the violence.

“This was an attack on the community, an attack on the peace process and an attack on the Good Friday agreement,” said Michelle O’Neill, the deputy leader of Sinn Féin, one of the two largest political parties in Northern Ireland, predominantly supported by Roman Catholics. Sinn Féin is a left-wing party and historically associated with the Provisional IRA.

O’Neill called on dissident groups to disband.

Northern Ireland’s other major party, the predominantly Protestant Democratic Unionist Party, also condemned the violence. The DUP is a right-wing party that was associated with pro-British paramilitary groups during the Troubles.

Its leader, Arlene Foster, called McKee’s death “heartbreaking news” and “a senseless act.”

“Those who brought guns onto our streets in the ’70s, ’80s and ’90s were wrong. It is equally wrong in 2019,” she said, referring to violence during the Troubles. “No one wants to go back. My thoughts are also with the brave officers who stood in defense of their community.”

U.S. House Speaker Nancy Pelosi was visiting Northern Ireland on Thursday when the riot broke out. She is in the country to commemorate the 21st anniversary of the Good Friday agreement, a peace treaty that helped end the Troubles. She condemned the violence.

(Courthouse News reporter Cain Burdeau is based in the European Union.)