Allen was shot in the head during fighting between the South Sudan army and rebel forces loyal to First Vice President Riek Machar along the country’s border with Uganda.
He was embedded with the opposition groups prior to his death.
On Monday, South Sudan’s minister of cabinet affairs Martin Elia Lomuro announced the formation of a committee to investigate the killing.
In a statement on Friday, the US and UK embassies in Juba welcomed the formation of an investigation committee and it must be followed by a thorough and credible investigation.
“The transitional government’s formation of a committee to investigate the death of journalist Christopher Allen more than six years after his death on August 26, 2017, is a long-awaited step in the right direction,” the statement extended to Sudans Post reads in part.
“The formation of a committee must be followed by a thorough investigation that is credible. Its findings must be made public and lead to accountability,” it added.
Despite international calls for justice in Allen’s case, South Sudan government described the journalist at some point as a “white rebel”.