The US State Department on Thursday condemned the release of Abdelraouf Abuzeid by the Sudanese high court earlier this week.
Abuzeid was found guilty of killing US diplomat John Granville and his driver, Abdel Rahman Abbas, in 2008.
“We call on the Sudanese government to exercise all available legal means to reverse this decision and to rearrest Abuzeid,” said State Department spokesman Ned Price.
Mr Price said John Godfrey, the US ambassador to Sudan, was “engaging Sudanese officials at the highest levels” on the matter.
Peter Lord, deputy assistant secretary of state for East Africa, Sudan and South Sudan, will travel to Khartoum next week to speak with Sudanese officials on Abuzeid's release.
Mr Granville was being driven home from a New Year’s Eve party at the British embassy 15 years ago when his car was ambushed.
According to reports, two gunmen sprayed 17 bullets into his car, killing both Mr Granville and Mr Abbas.
In 2020, the Sudanese government made a multimillion-dollar settlement with the family members of the victims, according to Reuters.
Mr Price refuted claims made by Abuzeid's brother that the 2020 deal paved the way for his release.
“The 2020 US Sudan bilateral settlement of legal claims did not address Abuzeid's imprisonment, or sentence,” he said.