The family and friends of a young journalist who was killed while covering the civil war in South Sudan have held a vigil on the anniversary of his death as they campaign for an investigation by the British and American governments into the lethal shooting.

Christopher Allen, who held held British and American nationality, was gunned down two years ago when he was just 26 while reporting on rebel forces fighting government forces. Images of his stripped body were subsequently posted on social media before being taken down after protests to the South Sudan government.

Mr Allen's relatives and colleagues say that repeated attempts to find out how and why he was killed have failed, with no adequate answers from the South Sudanese government, the Foreign Office in London and the State Department in Washington.

The gathering, held on Sunday outside the South Sudanese embassies in London and Washington to commemorate the death, starts a new phase in the quest, say campaigners, to obtain justice for Mr Allen.

The London legal firm, Doughty Street Chambers, are due to present a report this week outlining why the UK and US governments, as well as the South Sudanese government, must hold an inquiry into the killing and lay out the path to possible future legal action.

Mr Allen, who was a freelance journalist, had reported for news organisations including The Independent, Telegraph, al Jazeera and Vice, from a number of conflict zones.

There are conflicting accounts of Mr Allen’s death on 26 August 2017 in Kaya, a town near the Congolese and Ugandan border. The South Sudanese government does not admit culpability, but according to a number of reports, government troops say he was shot during a firefight with members of the rebel South Sudan People’s Liberation Movement in Opposition (SPLM-IO).

These soldiers claim they thought that Mr Allen was a “white mercenary” fighting alongside the rebels, despite despite reports that he was seen using a camera, not a gun.

The South Sudanese government denied that Mr Allen was the victim of a targeted killing. Government spokesman Michael Makuei said, however, in the aftermath of the death that the journalist had been previously denied entry into the country because of his “hostile reporting".

Mr Makuei said that Mr Allen had been reporting on the activities of opposition fighters loyal to former vice president Riek Machar, accompanied them into action, and this his government cannot bear any responsibility over the death.

Mr Machar returned to the South Sudan in October 2018 following a peace deal with the government. He is now living in Khartoum, the capital of Sudan, the state from which South Sudan seceded, following a delay in the implementation of a power-sharing agreement which was meant to come into effect on 12th May 2019.

Jeremy Bliss, a cousin of Mr Allen, said: “Sadly, there has been no meaningful effort by either the UK or the US government to press for an investigation into Chris’s death. We have made repeated approaches, but basically been fobbed off.

While the details on Allen's final moments remain vague, what is clear is that he was shot several times at close range (Chris Allen)

“We feel there is a duty for the British and American government to find out how one of their citizens was killed. We also have the issue of safety of journalists who take great personal risks to report on what is going on in dangerous places and the need to ensure that those who harm them are brought to account.

“Immediately after Chris’s death images of his naked body was posted on social media. We managed to get them taken down after protesting to the South Sudanese government and after American diplomats intervened. The FBI helped repatriate Chris’s body and they have investigatory powers over the deaths of US citizens. So there are ways of finding out the truth of what happened.”

Mr Bliss, a filmmaker, knew Paddy Ashdown, and the late former Liberal Democrat leader had helped raise questions by the Liberal Democrat peer, Baroness Northover, in the House of Lords.

A British diplomat aware of the situation surrounding Mr Allen’s death insisted that efforts to establish what took place have continued behind the scenes. The US ambassador to South Sudan, Thomas Hushek, said earlier this year: “The United States, with support from the UK, has been raising the investigation as a bilateral issue with South Sudan’s government. Whenever there’s an American citizen that dies overseas, anything that’s unusual you of course want to find out all the facts and report them back to the family."

But Rebecca Vincent, the UK Bureau Director of Reporters, said: "This overwhelming institutional failure to respond to the horrific killing of Christopher Allen in South Sudan two years ago is an outrage. Despite Chris' British and American citizenship, and despite the gravity of a journalist being killed in the line of duty, the UK and US governments have shamefully failed to meaningfully act or provide his family with anything other than bare minimum consular support.