Londonderry/Derry, Northern Ireland (CNN) Northern Ireland police have arrested two teenagers in connection with the murder of 29-year-old investigative journalist Lyra McKee, authorities said Saturday.

The men, aged 18 and 19, were arrested under the terrorism act, the Police Service of Northern Ireland (PSNI) tweeted. They have been taken to a police station in central Belfast.

Police are investigating whether they acted with others.

McKee, a prominent freelance journalist who wrote for publications including The Atlantic and Buzzfeed News, was killed in the Creggan area of Londonderry, also known as Derry, on Thursday night in what police described as a "terrorist incident."

Police said the shooting was carried out by dissident republicans, namely the New IRA.

"I believe both of those [arrested suspects] are members of the new IRA and I believe both were involved in the attack on Lyra," Detective Superintendent Jason Murphy said at a press conference Saturday as he appealed for eye witnesses to come forward.

"Lyra was killed by shots that were fired indiscriminately," he said. "The gunman showed no thought for who may have been killed or injured when he fired these shots.

"I know there will be some people who know what happened but are scared to come forward. I want to reassure you that we will work with you sensitively."

The PSNI released CCTV footage of the shooting in the hope that members of the public would provide information to assist the investigation into McKee's murder.

Detectives investigating the murder of Lyra McKee release CCTV footage and ask people to come forward with information. Call us on 101. https://t.co/Z1GP93HLLl — PSNI DC&S District (@PSNIDCSDistrict) April 19, 2019

The footage apparently captures McKee's final moments at around 10 p.m. local time (5p ET) on Thursday, when she stood among a crowd and raised her phone in the air to capture the rioting taking place in front of her.

McKee was standing close to a police vehicle when she was wounded by the shots fired by a single gunman. She died soon after from her injuries, assistant chief constable Mark Hamilton told reporters Friday.

"I cannot stress enough how important it is that people who were in the area last night and who recorded video and took photos share what they have with us," Murphy said in a statement on Friday.

In 2016, Lyra McKee was named as one of Forbes Magazine's 30 under 30.

"People saw the gunman and people saw those who goaded young people out onto the streets, people know who they are. The answers to what happened last night lie within the community. I am asking people to do the right thing for Lyra McKee, for her family and for the city... help us stop this madness."

'Single barbaric act'

McKee, who was born in Belfast, is the first journalist to be killed in the United Kingdom since 2001, according to nonprofit organization the Committee to Protect Journalists.

During a vigil on Friday, her partner, Sara Canning, said McKee's "amazing potential was snuffed out by this single barbaric act."

"Victims and LGBTQIA community are left without a tireless advocate and activist and it has left me without the love of my life, the woman I was planning to grow old with," she added.

"This cannot stand. Lyra's death must not be in vain because her life was a shining light in everyone else's life and her legacy will live on and the life that she has left behind."

In a rare joint appearance Friday, Democratic Unionist Party (DUP) leader Arlene Foster and Irish republican Sinn Fein party leader Mary Lou McDonald condemned the killing.

Thursday night's violence came ahead of Easter weekend, during which some republicans mark the anniversary of the 1916 Easter Rising, considered one of the most important events in the struggle for Irish independence from Britain.

Trouble flared when police entered the Creggan area in Londonderry to carry out searches among dissident republicans who were storing firearms and explosives for a number of planned attacks over Easter weekend, police said in a statement.

As the searches began, a crowd gathered and "upwards of 50 petrol bombs were thrown at officers," the statement said. Two vehicles were hijacked and set on fire, it added.

Flowers and tributes are left near the spot where Lyra McKee was shot on Thursday night.

A recent spate of unrest in Northern Ireland has raised fears that sectarian violence might be revived amid ongoing concerns over the effects of Brexit.

In January, a car bomb was detonated in Londonderry in a suspected attack by the New IRA.

Many fear that Britain's departure from the European Union will mean the reintroduction of border posts on the frontier between Northern Ireland, part of the UK, and the Republic of Ireland, a European Union member.

Border infrastructure was often targeted by Irish republican paramilitaries during the "Troubles," the decades-long sectarian conflict in which more than 3,500 people died.