Northern Ireland Journalist Is Killed in Street Clash

The police in Northern Ireland said a journalist was killed Thursday during a night of unrest in the city of Londonderry in which gasoline bombs were thrown and shots fired.

Mark Hamilton, an assistant chief constable, called the killing of the journalist, 29-year-old Lyra McKee, “‘horrendous and unjustified.”

The police considered the killing to be a “terrorist incident” and said they had begun a murder investigation. Mr. Hamilton said a single gunman had opened fire in a residential neighborhood, hitting Ms. McKee, who later died from her injuries.

Although the police have not ascribed a motive to the attack that led to Ms. McKee’s death, the burst of violence was a reminder of the sectarian violence that plagued Northern Ireland until a peace agreement was signed in 1998.

“It’s important that we all stand together now and resist any further escalation of this,” Mr. Hamilton said. He added that the police were carrying out searches in the area on Thursday because of concerns that “violent dissident republicans were storing firearms and explosives.”

Ms. McKee grew up on Cliftonville Road in Belfast, near the area that saw some of the worst violence during the Troubles, the three decades of violence that preceded the 1998 Good Friday Agreement, which largely brought an end to the conflict. Her work often examined the legacies of that era of tensions between Catholics and Protestants.

A local journalist, Leona O’Neill, wrote on Twitter that she was standing beside a woman at the site of the violence Thursday night when the woman fell beside a police vehicle. She said the police immediately put the woman in the back of their vehicle and took her to a hospital.

In her Twitter feed, Ms. O’Neill described people throwing gasoline bombs, bricks and bottles at the police in the Creggan area of the city. Videos showed vehicles on fire.

She said people had gathered in the streets after a large number of police officers had begun to search a home in the area.

After violence erupted, the police appealed for calm.

The killing happened after Speaker Nancy Pelosi visited the city earlier in the day to show support for the peace agreement that the United States helped broker two decades ago.

The prospect that Britain might leave the European Union without an agreement has raised the prospect that a so-called border would be re-established between the Irish Republic and British-governed Northern Ireland, and Ms. Pelosi said it was vital to keep a “seamless border” after Brexit.

Sinn Fein, the former political wing of the Irish Republican Army, and the pro-British Democratic Unionist Party condemned the killing of Ms. McKee. Sinn Fein called it an “attack on all the community.”

Ms. McKee is author of a book, “Angels With Blue Faces,” about the 1981 murder of Rev. Robert Bradford, a member of Parliament from Belfast.

Last year she signed a two-book deal with publishing house Faber & Faber. One of those books investigates the disappearances of young men in Belfast in the late 1960s and 1970s. The book, titled The Lost Boys, was scheduled to come out next year.

“McKee has that knack of engaging the head and the heart — the fate of these children is deeply affecting and we’re engaged too with her argument that these missing children tell us something of a whole lost generation, that of the ‘cease-fire babies,’” Laura Hassan, editorial director at Faber, said last year.

Her last tweet showed a photo of a crowd of people, police trucks and smoke rising in the distance, with the words, “Derry tonight. Absolute madness”