The paramilitary Rapid Support Forces (RSF) group, which has been engaged in a two-year war with Sudan's army, has been entirely pushed out of Khartoum state, says the military.
"Khartoum State is completely free of rebels", the army said in a statement published by Sudan's News Agency.
The announcement comes nearly two months after the military recaptured Khartoum city - including the presidential palace - from its rivals in a major victory.
Earlier on Tuesday, fighting had broken out between the warring groups in the city of Omdurman - which is also in Khartoum state and part of the capital region.
The army said on Monday that it had started a "large-scale offensive" in Omdurman, according to the AFP news agency.
The RSF has not yet commented on the army's latest claim.
Khartoum had once been at the heart of Sudan's government, but the country's military leaders were forced to move east to Port Sudan after their rivals took control of the area.
Until recently Port Sudan had been viewed as relatively safe, however it was at the centre of escalating fighting when it came under drone attack earlier this month, which the army blamed on the RSF.
The attacks hit key infrastructure and led to water shortages and worsening blackouts.
The war has also had diplomatic reverberations, with relations souring between Sudan and the United Arab Emirates (UAE), after Sudan accused the gulf nation of supporting the RSF, which it denies.
Those accusations continued on Tuesday, with Sudan saying the UAE was responsible for an attack on Port Sudan earlier this month, Reuters news agency reported.
The UAE has strongly denied the accusations, describing them as "unfounded allegations".
Since the civil war erupted three years ago, thousands of people have died and millions have been displaced from their homes - creating the world's worst humanitarian crisis.
Both the army and the RSF have been accused of war crimes, which they deny.
