Police in Northern Ireland have arrested two teenagers in connection with the fatal shooting of journalist Lyra McKee. The men, aged 18 and 19, were detained Saturday under anti-terrorism legislation and taken to Belfast for questioning, the Police Service of Northern Ireland said.

The men have not been identified or charged. Police had said earlier there was one gunman who pulled the trigger who had been backed by an "organization," and said they were searching for multiple suspects.

McKee, 29, was a rising star of investigative journalism. She was killed during rioting in the city of Londonderry Thursday night, probably by a stray bullet aimed at police. Police called it a "terrorist act" and said the New IRA dissident group was most likely responsible.

Lyra McKee

The rioting broke out after the Northern Irish police, fearing violence over the weekend, conducted a series of raids searching for weapons and ammunition.

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The use of a firearm apparently aimed at police marks a dangerous escalation in sporadic violence that continues to plague Northern Ireland 21 years after the Good Friday peace agreement was signed. Assistant Chief Constable Mark Hamilton said earlier that a gunman fired a number of shots at police during the unrest.

Police on Friday night released closed-circuit TV footage showing the man suspected of firing the shots that killed McKee. The footage shows the police facing a barrage of gasoline bombs before the shots were fired by someone wearing a balaclava to obscure his face.

Hours before her death, McKee tweeted a photo of the rioting with the words: "Derry tonight. Absolute madness."

The killing was condemned by all the major political parties as well as the prime ministers of Britain and Ireland. The European Union's chief Brexit negotiator, Michel Barnier, said it was "a reminder of how fragile peace still is in Northern Ireland" and called for work to preserve the Good Friday peace agreement.

The New IRA, a small group, rejects the agreement, a peace accord that ended decades of violence between those who wanted Northern Ireland to remain a part of the United Kingdom and and those who wanted it to leave. The New IRA is regarded as the largest of the splinter dissident groups still operating and has been linked to several other killings in the past decade.

Catholic priest Joseph Gormley, who administered the last rites to McKee in the hospital, told the BBC the rioting Thursday was "clearly orchestrated" by a "small group of people who want to play political games with our lives and want to use our community as a place where they can play their little war games."

Some politicians believe uncertainty over Brexit and the possible re-introduction of a "hard border" between Northern Ireland and the Republic of Ireland are stoking tensions in the region.

McKee was seen as a rising star, named to Forbes "30 under 30" list of notable media figures in 2016. She had written for BuzzFeed and the Atlantic, and recently signed a deal to write two books, CBS News' Haley Ott reported.

She rose to prominence in 2014 with a moving blog post -- "Letter to my 14 year old self" -- describing the struggle of growing up gay in Belfast, the capital of Northern Ireland. She described the shame she felt at 14 as she kept the "secret" of being gay from her family and friends, and the love she eventually received when she was finally able to reveal it.

Her partner, Sara Canning, told a vigil Friday that McKee's amazing potential had been snuffed out. Canning said the senseless murder "has left me without the love of my life, the woman I was planning to grow old with."

"It has left so many friends without their confidante," she added.