After days of conflict between a known paramilitary group and the national army, gunfire and explosions have been heard in the capital city of Sudan, Khartoum.
The dispute centres around a proposed transition to civilian rule.
Reuters is reporting that gunfire has been heard close to the headquarters of the army in the centre of the city.
The paramilitary Rapid Support Forces (RSF) says it has taken control of the airport and presidential palace.
These claims have not been confirmed.
Earlier the RSF had said that one of its camps in the south of Khartoum had been attacked.
For its part, the army has said that RSF fighters have been trying to seize the military headquarters.
“Fighters from the Rapid Support Forces attacked several army camps in Khartoum and elsewhere around Sudan,” the AFP news agency quotes army spokesman Brig Gen Nabil Abdallah as saying.
“Clashes are ongoing and the army is carrying out its duty to safeguard the country.”
The Reuters news agency is also citing witnesses as saying that there was gunfire in the northern city of Merowe.
Alarabyia TV is broadcasting pictures of smoke rising from a military camp there, Reuters reports.
Generals have been running the country, through what is called the Sovereign Council, since a coup in October 2021.
The RSF is under the command of the council’s vice-president Gen Mohamed Hamdan Dagalo. The army, meanwhile, is led by Gen Abdel Fattah al-Burhan, who is the head of the Sovereign Council.
A proposed move to a civilian-led government has foundered on the timetable to integrate the RSF into the national army.
The RSF wanted to delay it for 10 years, but the army said it should happen in two years.
On Thursday, the RSF deployed forces near the military base in Merowe as tensions increased this week.
Gen Burhan said he was willing to talk to his second in command to resolve the dispute over who would lead a unified army in a proposed civilian government.
Western powers and regional leaders had urged the two sides to de-escalate tensions and to go back to talks aimed at restoring civilian rule.
There had been signs on Friday that the situation would be resolved.
In a tweet, US Ambassador John Godfrey said: “I urgently call on senior military leaders to stop the fighting.”
Describing the situation in the city, he said he “woke up to the deeply disturbing sounds of gunfire and fighting. I am currently sheltering in place with the Embassy team, as Sudanese throughout Khartoum and elsewhere are doing.”
Russia’s embassy is also concerned by the “escalation of violence” and has urged a ceasefire, Reuters reports.
The 2021 coup ended a period of more than two years when military and civilian leaders were sharing power. That deal came after Sudan’s long-term authoritarian President Omar al-Bashir was overthrown.
There have been regular pro-democracy protests in Khartoum ever since the coup.