The source, who spoke on condition of anonymity because they were not authorised to brief the media, said RSF drones "targeted the headquarters of the army's 17th Infantry Division in Sinja, the capital of Sennar state".
Sennar state has seen relative calm since the army recaptured key Sudanese cities in late 2024 in an offensive that later saw it regain the capital Khartoum.
The Sennar region was last targeted by drones in October.
One resident of Sinja told AFP on Monday that they "heard explosions and anti-aircraft fire".
Sinja, which is located around 300 kilometres (180 miles) southeast of Khartoum, lies on a road linking army-controlled areas of eastern and central Sudan.
The strike comes a day after the army-aligned government said it had returned to Khartoum following three years operating from its eastern wartime capital of Port Sudan.
In the early days of the National military's war with the paramilitary Rapid Support Forces (RSF) in April 2023, the army-aligned government fled the capital, which was quickly overrun by rival troops.
"Today, we return, and the Government of Hope returns to the national capital," Idris told reporters in Khartoum, promising "better services" for residents.
For close to two years, the Sudanese capital, composed of the three cities of Khartoum, Omdurman, and Khartoum North (Bahri), was an active battlefield.
The Sudanese army has been battling the RSF militias since April 2023 in a war that has killed tens of thousands of people and displaced millions, according to international agencies.
In October, reports of mass atrocities committed by the RSF against civilians emerged after the militia seized North Darfur's city of El-Fasher, triggering regional and global condemnation.
In November, rights group Amnesty International also accused the RSF of committing "war crimes" in El-Fasher, ranging from the summary execution of unarmed men to the rape of girls and women.
Humanitarian agencies warn that Sudan is facing what they describe as the world’s largest humanitarian crisis. Across the country, nearly 26 million people -- around half the population -- are facing acute hunger, according to the United Nations.
Famine has been declared in parts of El Fasher and Kadugli, with an imminent risk of famine identified in 20 other locations across Darfur and Kordofan through January 2026, according to international assessments.
The Quad mechanism, which includes Egypt, Saudi Arabia, the United Arab Emirates and the United States, has been working to mediate a peaceful resolution to the conflict in Sudan.
Cairo has reiterated its support for Sudan’s internationally recognised government and stressed its categorical rejection of any attempts to violate the country’s sovereignty or territorial integrity.
In November, Sudan’s army chief and head of the Sovereignty Council, Abdel Fattah Al-Burhan, has praised an initiative launched by Saudi Crown Prince and Mohammed bin Salman to help resolve the conflict. The following month, Khartoum said Al-Burhan was ready to work with US President Donald Trump to halt the war in Sudan.
* This story was edited by Ahram Online.
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