Sudan's army launched artillery and air strikes in Sudan's capital on Thursday in its biggest operation to regain ground there since early in its 17-month war with the Rapid Support Forces (RSF), witnesses and military sources said.

The push by the army, which lost control of most of the capital at the start of the conflict, came ahead of an address by its commander, General Abdel Fattah al-Burhan, at the United Nations General Assembly in New York later in the day.

Witnesses reported heavy bombardments and clashes as army troops tried to cross bridges across the Nile connecting the three adjoining cities that make up the greater capital, Khartoum, Omdurman and Bahri.

"The army is carrying out heavy artillery strikes and air strikes on Halfaya and Shambat," Ahmed Abdalla, a 48-year-old resident told Reuters by phone, referring to areas of Bahri close to the river. "The sounds of explosions are very loud."

Video footage showed black smoke rising above the capital and the booms of the battle could be heard in the background.

Army sources said their forces had crossed bridges in Khartoum and Bahri. The RSF told Reuters it had thwarted the army's attempt to cross two bridges to Khartoum. Reuters could not independently confirm the accounts.

Though the army retook some ground in Omdurman early this year, it depends mostly on artillery and airstrikes and has been unable to dislodge nimble RSF ground forces embedded in other parts of the capital.

DARFUR FEARS

The RSF has also continued to make advances in other parts of Sudan in recent months in a conflict that has caused a vast humanitarian crisis, displacing more than 10-million people and driving parts of the country to extreme hunger or famine.

Diplomatic efforts by the United States and other powers have faltered, with the army refusing to attend talks last month in Switzerland.

This month the battle for control of al-Fashir, the capital of North Darfur state in the west of Sudan, has also intensified as the RSF has tried to advance from positions surrounding the city against the army and allied former rebel groups.

Al-Fashir is the last army holdout across the Darfur region, where the UN and rights groups say the RSF and allies have led ethnically-targetted attacks and the humanitarian situation is particularly critical. The RSF has denied being behind the violence.

The UN human rights office said on Thursday it had documented summary executions, sexual and gender-based violence, and abductions of women and young men in al-Fashir, in addition to rising civilian casualties.

"From bitter past experience, if al-Fashir falls, there is a high risk of ethnically targeted violations and abuses, including summary executions and sexual violence, by the RSF and allied militia," UN Human Rights Chief Volker Turk said.

The UN Security Council and secretary-general have also demanded an end to the siege of al-Fashir, home to more than 1.8-million residents and displaced people.

The war began when tensions between the RSF and the army, who had been jostling for position ahead of an internationally-backed transition to civilian rule, erupted into open conflict.

The army and the RSF had previously shared power after staging a coup in 2021, two years after veteran autocrat Omar al-Bashir was toppled in a popular uprising.