Amy chief Gen Abdel Fattah Al Burhan, meanwhile, formally asked UN Secretary General Antonio Guterres to replace his envoy Volker Perthes, according to a statement by the ruling Sovereign Council.
Mr Perthes, the UN envoy to Sudan since 2021, had spearheaded an international campaign to restore Sudan's democratic transition, upended by a 2021 coup led by Gen Al Burhan and his deputy-turned-enemy Gen Mohamed Dagalo of the Rapid Support Forces.
In his letter to Mr Guterres, Gen Al Burhan claimed that the UN envoy operated outside the boundaries of his mandate and blamed him for indirectly encouraging the RSF to stage its “mutiny”.
He also accused Mr Perthes of misleading the UN about the political situation in Sudan.
Mr Guterres said he was shocked by Gen Al Burhan's request and he has full confidence in Mr Perthes, a German.
"The Secretary-General is proud of the work done by Volker Perthes and reaffirms his full confidence in his Special Representative," UN spokesperson Stephane Dujarric said
The envoy's push for the restoration of the transition and a civilian-led government was known to be opposed by some in the army.
He led months of tortuous negotiations that produced a preliminary agreement in December that provided for the army to quit politics and a civilian to lead a 24-month transitional government until elections are held.
It also provided for the RSF's integration into the army, something that Gen Dagalo is known to have resisted.
Negotiations to reach a permanent settlement were derailed when fighting broke out between the army and the RSF on April 15.
The decision to call up reservists and retired soldiers, meanwhile, appeared to be aimed at bolstering the army's ranks as it battles the RSF.
It also underlines the resolve of Gen Al Burhan to dig in for a long fight.
Sudan's Ministry of Defence, meanwhile, called on retired soldiers to head to the nearest army base to be given a firearm to protect themselves and their families against what it called attacks by RSF fighters on civilians and to fend off looters.
Widespread looting in Khartoum is widely blamed on the RSF and criminal gangs.
Sporadic fighting in Khartoum has continued all week despite a seven-day ceasefire that came into effect on Monday.
Ceasefire monitors Saudi Arabia and the US, however, said earlier on Friday that compliance was improving, but the army moves may indicate it is gearing up for a long conflict.
About 1.3 million people have fled their homes, either across borders or within the vast Afro-Arab nation.
The Ministry of Health has said at least 730 people have died, though the true figure is likely to be much higher.