The dissident republican group, the New IRA, has admitted responsibility for the killing of Lyra McKee offering “full and sincere apologies” to her family and friends.

In a statement to the Irish News using a recognised codeword, the group acknowledged its activists had killed the 29-year-old investigative journalist and reporter, who was shot dead in the Creggan estate in Derry on Thursday, and apologised to her relatives.

However, it also sought to justify its actions, characterising them as part of a defensive operation against enemy forces.

The statement read: “On Thursday night, following an incursion on the Creggan by heavily armed British crown forces which provoked rioting, the IRA deployed our volunteers to engage. We have instructed our volunteers to take the utmost care in future when engaging the enemy, and put in place measures to help ensure this.

“In the course of attacking the enemy Lyra McKee was tragically killed while standing beside enemy forces. The IRA offer our full and sincere apologies to the partner, family and friends of Lyra McKee for her death.”

The statement followed a protest on Monday by McKee’s Friends outside the Derry offices of Saoradh, a republican party that reflects New IRA thinking.

Several of the protesters smeared red handprints on the walls and on a republican sign at the Derry headquarters of the party to symbolise their claim that it had blood on its hands over the killing.

Some supporters of Saoradh stood around the Junior McDaid House building during the protest but did not intervene. They remained silent with their arms folded in defiance as reporters and TV news crews watched.

Sinead Quinn, one of those who took part in the protest, criticised Saoradh for attempting to blame McKee’s death last Thursday on an accidental shooting.

“Lyra McKee was an investigative journalist, she deserves more,” she said. “I’m so glad to see that there are so many people here today and watch these men standing there looking at us women. That’s not a representation of the republican people of this town. Nobody can advocate shooting into a crowd of people.”

Emotions running high in Derry as friends of #LyraMcKee protest with red paint at HQ of Saoradh, linked with New IRA pic.twitter.com/jaZuKzGnQk — Stephen Murphy (@SMurphyTV) April 22, 2019

Police officers allowed the protest to go ahead after offering advice to those taking part.

Friends of slain journalist Lyra McKee have put red paint handprints over the front of dissident republican HQ Junior McDaid House in #Derry in protest over the murder of the 29-year-old #LyraMcKee pic.twitter.com/jzhnTM0GcX — Leona O'Neill (@LeonaONeill1) April 22, 2019

Supt Alan Sutton of the Police Service of Northern Ireland (PSNI) said: “At this time, police have not received any complaints in relation to the protest.”

The protest came after Irish politicians and clerics turned Easter Rising commemorations into a platform to condemn dissident republicans for McKee’s killing. The taoiseach, Leo Varadkar, said Saoradh’s response to her death was “beneath contempt”.

On Sunday two men in their late teens who had been arrested over the killing were released without charge. The PSNI continues to appeal to the Creggan community for help and is exploring ways to protect witnesses.

McKee was killed after trouble flared at about 9pm last Thursday when police entered Creggan to search for guns and explosives to avert possible terror attacks over the Easter weekend, when republicans commemorate the 1916 Easter Rising.

Youths responded by throwing dozens of petrol bombs as well as bottles and other missiles, and vehicles were set on fire. Security cameras and mobile phone footage captured a masked gunman opening fire in the direction of police vehicles where McKee and others were standing.

A PSNI spokesman confirmed the service was exploring the option of allowing witnesses to give evidence behind screens or through video.

Det Supt Jason Murphy said: “We have received very positive support from the community but we need to convert this support into tangible evidence that will enable us to bring Lyra’s killers to justice. We will continue to work positively and sensitively with the local community to achieve this.”

McKee’s funeral will be held at St Anne’s Cathedral in Belfast on Wednesday. Her partner, Sara Canning, said the service would be a “celebration of her life”.

McKee’s publisher, Faber and Faber, which commissioned her to write a book about the disappearances of a number of children and young men in Northern Ireland, urged her supporters to wear Harry Potter or Marvel-themed costumes.