Activists say at least 50 people have died since demonstrations began last month.
Organisers behind anti-government demonstrations in Sudan said security forces have killed at least five protesters in the last 24 hours, a claim disputed by the government.
A protest on Saturday saw one of the largest turnouts in more than three months of demonstrations calling on President Omar al-Bashir to resign.
The protests began in December in reaction to spiralling prices and a failing economy but quickly escalated into demands for al-Bashir’s departure after three decades in power.
Sarah Abdel-Jaleel, a spokesperson for the Sudanese Professionals Association, told The Associated Press news agency on Sunday that four people were killed in the capital city of Khartoum when security forces tried to disperse crowds approaching the military’s headquarters.
Another protester was killed in Omdurman, the twin city of Sudan’s capital, Abdel-Jaleel said.
State-run SUNA news agency quoted police spokesman General Hashim Abdel-Rahim as saying that one person was killed “during disturbances in Omdurman”.
Officials say 31 people have died in protest-related violence so far, but Human Rights Watchhas put the death toll at 51, including children and medics.
Reaching army HQ
Chanting “one army, one people”, protesters heeded a call by the organisers to march on the army headquarters, located near al-Bashir’s residence.
Witnesses told Reuters news agency that security forces used tear gas to disperse the demonstrators, some of whom were reportedly arrested.
SUNA said civilians and policemen were injured in the demonstrations, citing police reports as thousands of protesters clashed with security forces near the president’s residence.
On February 22, al-Bashir imposed a nationwide state of emergency after an initial crackdown failed to rein in demonstrators.
Since the emergency rule came into effect, protests have been largely confined to the capital and Omdurman.
But organisers had called for widespread rallies and a march on the army headquarters on Saturday, the 34th anniversary of the 1985 uprising that toppled the then-government of President Jaafar al-Nimeiri.
The military removed al-Nimeiri before handing over power to an elected government, which in turn was overthrown by al-Bashir in a 1989 coup.
Before the demonstrations began, security forces were deployed in large numbers at key squares in Khartoum and Omdurman across the Nile.
Witnesses said plain-clothes security agents were preventing even passers-by from reaching central areas.
Shops and markets in central Khartoum were ordered shut before the march by security agents, according to onlookers.
The protest movement was initially led by the Sudanese Professionals Association, but several political parties, including the main opposition National Umma Party, have taken part since.
Analysts say the movement has emerged as the biggest challenge yet to al-Bashir’s rule.
However, the veteran leader has remained defiant and has introduced tough measures that have seen protesters, opposition leaders, activists and journalists arrested.