Sudan's army has confirmed that the rival Rapid Support Forces (RSF) have taken the main base of a well-equipped police brigade in the capital Khartoum.
It comes amid reports of fighting spreading for the first time to Blue Nile state near Ethiopia.
The RSF said it had captured dozens of armoured vehicles and pickup trucks after seizing the Central Reserve Police headquarters yesterday, consolidating its position in southern Khartoum where several important military camps are situated.
The army had leant on the Central Reserve Police for ground fighting in Khartoum, where it has struggled to counter mobile RSF units which quickly spread out across the city once fighting erupted on 15 April.
The army said in a statement that the Central Reserve police base had been taken after three days of fighting, accusing the RSF of attacking "state institutions".
Local activists said at least 15 civilians had been killed in the fighting, and more than 80 had been seriously injured.
Also today, residents on social media reported an attack by the SPLM-N, Sudan's most powerful rebel group, in the city of Kurmuk in Blue Nile State, on the border with Ethiopia.
The United Nations mission in Sudan said hundreds of civilians had crossed the border into Ethiopia to seek safety due to clashes in Blue Nile yesterday and today, while others appeared set to head north to Damazin, the state capital.
Clashes linked to tribal tensions in Blue Nile State left hundreds dead last year.
The SPLM-N last week clashed with the army in South Kordofan state, raising fears the conflict could spread across Sudan's southern regions.
The war between the army and the RSF erupted amid disputes over internationally backed plans for a transition towards elections under a civilian government.
Fighting has intensified through a series of ceasefire deals negotiated by Saudi Arabia and the United States at talks in Jeddah that were suspended last week.
The war has caused a major humanitarian crisis, uprooting more than 2.5 million people, about 600,000 of whom have crossed into neighbouring countries.
Most have headed north to Egypt or west into Chad, where refugees have sought shelter from ethnically motivated attacks and clashes in Sudan's Darfur region.
Some families will spend the Muslim holiday of Eid al-Adha this week far away from their relatives.
"It's the first time I spend Eid away from Sudan and alone," said Safiya Juma Adam, who fled the war to Giza in Egypt with her three children.
"If it weren't for this war, I wouldn't have left Sudan."
