A floral tribute Saturday at the scene where journalist Lyra McKee was fatally shot Thursday in Londonderry, Northern Ireland. (Paul Faith/AFP/Getty Images)

Two teenagers are under arrest in Northern Ireland in connection with the shooting of a 29-year-old journalist who was killed during riots Thursday evening.

Police in Northern Ireland said Saturday that the two suspects, ages 18 and 19, were arrested under a terrorism law and taken to Belfast for questioning. They had not been identified, but on Friday police said they believed the New Irish Republican Army was responsible for her death.

The victim, Lyra McKee, was covering Thursday’s riots in the border town of Londonderry, also known as Derry, when she was struck by at least one bullet. Shots were also fired at police. The last tweet she sent out before she was killed showed a photo of the violent scene, with the caption: “Derry tonight. Absolute madness.” Clashes broke out after police carried out raids against suspected militant Irish nationalists.

McKee was killed nearly 21 years to the day after a 1998 peace treaty, known as the Good Friday Agreement, was signed, ending the Troubles, the long period of violence in Northern Ireland in which Irish nationalists battled with United Kingdom loyalists and British troops. She was working on a book about young people who disappeared during the Troubles.

The riots took place in a neighborhood of Londonderry that is home to a large number of Irish nationalists. Although widespread violence in Northern Ireland came to an end decades ago, tensions have not entirely de-escalated. In January, a car bomb exploded in Londonderry.

On Saturday, Detective Superintendent Jason Murphy told reporters that he had “just come from a very difficult meeting with Lyra McKee’s family and her partner and, as you can imagine, they are absolutely devastated.”

The shots fired at McKee were “fired indiscriminately,” Murphy said. “The gunman showed no thought for who may have been killed or injured when he fired these shots.”

He appealed for people who witnessed the riots to provide cellphone footage to detectives. “I know there will be some people who know what happened but are scared to come forward,” he said.

On social media, police released closed-circuit TV footage of the riots and asked viewers to send in information. The footage identifies McKee standing toward the back of a crowd, raising her phone to capture video.

On Friday, Mark Hamilton, assistant chief constable of the Police Service of Northern Ireland, said officials “believed that violent dissident republicans were planning attacks in this city, and we were looking for munitions and firearms that we believe may be about to be used across the Easter weekend.”

McKee’s family and friends held a vigil to honor her Friday. Her partner, Sara Canning, called her death a “senseless murder” and said she was “the woman I was planning to grow old with.”

Irish Prime Minister Leo Varadkar called her killing “an attack on all of us, our nation and our freedoms.”

Amanda Ferguson in Belfast contributed to this report.

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