The New IRA have a modern-sounding name, but the shooting of Lyra McKee harks back to a strand of atavistic Irish republicanism.

According to this worldview, it was not a reckless gunman from a tiny, fringe terrorist group who killed the journalist during riots in Derry on Thursday night, but a freedom fighter who was resisting British imperialism.

A statement on the website of Saoradh, a political party that reflects New IRA thinking, blamed the death on an “incursion” by “heavily armed crown forces” in the Creggan estate.

“A republican volunteer attempted to defend people from the PSNI/RUC,” it said, citing the acronyms of Norther Ireland’s current and former police forces. “Tragically a young journalist, Lyra McKee, was killed accidentally.”

Few people in Northern Ireland accepted this quasi-apology from the breakaway dissident republicans.

“The murder of this young woman is a human tragedy for her family, but it is also an attack on all the people of this community, an attack on our peace process and an attack on the Good Friday agreement,” said Sinn Féin’s deputy leader, Michelle O’Neill.

For once in Northern Ireland’s polarised political landscape Sinn Féin, unionism and the police were in agreement. With ordinary people in Derry expressing shock and revulsion at the killing, the New IRA and Saoradh are facing a backlash.

“Indiscriminate firing was reckless and I think this incident will unite people, including many republicans, in condemnation of what happened here,” said Marisa McGlinchey, the author of Unfinished Business, an academic study of dissident republicans.

But the New IRA will almost certainly continue its campaign, she said. “I don’t suspect that it will affect their strategy in the long term.”

The rioting flared on Thursday night after police entered the Creggan estate searching for guns and explosives, which they said were being stored for planned attacks over the Easter weekend, when republicans mark the anniversary of the 1916 Easter Rising.

Two cars were set alight and dozens of petrol bombs thrown before a gunman opened fire in the direction of police vehicles, where journalists and other civilians were standing.

The New IRA emerged in 2012 via a merger of several groups opposed to the peace process, including the Real IRA. Police believe it has several hundred active supporters, a mix of former Provisional IRA members and new, young recruits, including some born after the 1998 Good Friday agreement.

The breakdown of power-sharing between Sinn Féin and the Democratic Unionist party in 2017 has left a political vacuum that been compounded by Brexit.

Dissidents are disenchanted with the peace process, saying it has parked the quest for Irish unity and legitimised rule by unionists who denigrate Irish identity. Poverty and joblessness fuel grievance.

The New IRA has been linked with the murder of two prison officers and multiple other attacks, including a car bomb outside Derry’s courthouse in January.

Many dissidents consider themselves the true heirs of a republican tradition predating the 1916 Easter Rising. According to this view, successive republican leaders such as Michael Collins, Eamon de Valera and Gerry Adams, who have made peaceful accommodation with the British state, are traitors. The breakaway revolutionaries who keep fighting are the true republicans – until they too forge accommodation with the British, triggering a fresh breakaway group, which perpetuates the cycle.

“Every generation, going back 800 years, Irish republicans have confronted British occupation,” Brian Kenna, the chairman of Saoradh, told the Guardian last month. “I don’t see any reason why that’s going to stop.”

Brian Kenna, chairman of the political party Saoradh, in Dublin Photograph: Rory Carroll/The Guardian

By reviving talk of a hard border, Brexit was a huge opportunity, he said. “It’s not the reason why people would resist British rule, but Brexit just gives it focus, gives it a physical picture. It’s a huge help.”

Security forces had infiltrated and surveilled republican ranks but resistance would continue and grow, said Kenna. “The republican movement is very adaptable. Necessity is the mother of invention.”

The campaign would be smaller than that waged by the Provisional IRA during the Troubles, but could still be “impactful” and “very difficult to stop”, he claimed.

A week after the interview, the New IRA was accused of sending letters with crude explosives to transport hubs in Britain. Saoradh representatives denied any knowledge of the letters.

In the absence of a militarised border or troops on the streets, republican socialist ideology was incentivising recruits, said Kenna. “Young people are now getting involved in an armed campaign without a personal experience of oppression,” he said.