A mourner wearing a Gryffindor scarf arrives for the funeral of murdered journalist Lyra McKee in Belfast. Brian Lawless/Reuters

The leaders of Britain and Ireland joined mourners from across Northern Ireland's political divide on Wednesday at the funeral of a young journalist killed by a dissident republican paramilitary group last week.

Lyra McKee, 29, who chronicled the troubled history of Northern Ireland, was shot in the head on Thursday as rioters clashed with police in Londonderry, the second biggest city of the British province.

Dissident republican faction the New IRA claimed responsibility on Tuesday and apologised, saying the shots had been aimed at the police.

The killing evoked memories of the three decades of violent strife in Northern Ireland and sparked condemnation across the political spectrum also in the neighbouring Republic of Ireland.

British Prime Minister Theresa May and Irish counterpart Leo Varadkar were among those who attended the ceremony, alongside the heads of the province's biggest unionist and nationalist political parties.

Britain's main opposition Labour leader Jeremy Corbyn also missed weekly Prime Minister's Questions in parliament to travel to Belfast for the funeral at St Anne's Cathedral.

"In death, Lyra has united people of many different backgrounds," Father Martin Magill told those gathered in a poignant tribute to McKee.

"I pray that Lyra's murder may be the catalyst needed for parties to start talking, to reform that which was corrosive... and to begin anew," he said.

Agence France-Presse