The US State Department has also summoned Sudan’s ambassador to Washington over the controversial release of the convict, Abdel Raouf Abu Zaid.

Zaid was facing the death penalty over the killing of diplomat John Granville and his Sudanese driver Abdel Rahman Abbas on New Year’s Day in 2008.

The US has described as false Sudan's claims that the family of Mr Granville had forgiven the killer.

The State Department denied that the release was part of an agreement between the two countries.

In 2020, Sudan’s transitional government agreed to pay about $335m (£274m) as compensation related to the 1998 bombings of the American embassies in Kenya and Tanzania, the attack on the USS Cole in Yemen in 2000 and the killing of Mr Granville.

Mr Granville and his Sudanese colleague Mr Abbas both worked for the US Agency for International Development in Sudan. They were shot and killed by gunmen as they left a New Year party in 2008.