Sudan on Sunday severed diplomatic relations with neighbouring Chad, Omdurman public radio reported, citing what it called Ndjamena's support for a Darfur rebel attack north of Khartoum.
"Sudan has cut diplomatic relations with Chad because of its support for the attack" on Saturday on the capital's twin city of Omdurman across the river Nile, the station said.
The government said earlier it had repulsed the assault by Justice and Equality Movement (JEM) rebels, allegedly backed by Ndjamena, which saw the insurgents reach Omdurman with the declared intent of toppling the regime.
Sudan, which declared an emergency curfew as JEM forces marched on the capital, was quick to accuse Chad of being behind the attack.
"The Justice and Equality Movement attempted to destabilise security but Sudanese forces opposed them," senior ruling party member Kamal Obeid Obeid said, blaming Chad for the fighting.
"The attempt by (Chadian) President Idriss Deby to destabilise Sudan has failed," Obeid said.
Khartoum and Ndjamena accuse each other of backing rebels seeking to topple their respective regimes.
The rebels "are now either dead or prisoners of war," army spokesman Brigadier General Osman al-Aghbash told public radio.
An unnamed security official told state television that Omdurman was "completely calm" on Sunday.
State television showed images of what it said were captured rebels cowering in the back of an armoured personnel carrier, along with footage of captured rebel all-terrain vehicles, field artillery and shells.
The JEM said on Saturday that its fighters had taken control of Wadi Saidna air force base about 10 miles (16 kilometres) north of Khartoum and were headed into the capital.
Witnesses said there was heavy fighting in Omdurman for at least two hours.
The White House said it was "very concerned" about the violence and urged both the Darfur rebels and government forces to cease hostilities.
A curfew was imposed in the capital until 0700 GMT on Sunday, the interior ministry said.
The extent of casualties in the fighting was not immediately known, although state television showed at least one body lying in the street.