The Sudanese army was Thursday planning to make "an important announcement", state media said, after months of protests demanding the resignation of longtime leader President Omar al-Bashir.
Thousands of Khartoum residents chanted "the regime has fallen" as they flooded the area around army headquarters where protesters have held an unprecedented sit-in now in its sixth day.
"The Sudanese army will issue an important statement soon. Wait for it," the state television anchor said, without giving further details.
Martial music replaced the television's normal programming.
The protests, which erupted in December, have become the biggest challenge yet to Bashir's three decades of iron-fisted rule.
"We are waiting for big news," one protester told AFP from the sit-in.
"We won't leave from here until we know what it is. But we do know that Bashir has to go.
"We had enough of this regime -- 30 years of repression, corruption, rights abuses, it's enough."
Crowds of demonstrators have spent five nights defiantly camped outside the sprawling headquarters complex, which also houses Bashir's official residence and the defence ministry.
There has been an often festive mood at the sit-in, with protesters singing and dancing to the tunes of revolutionary songs.
Several military vehicles carrying troops entered the compound in the early hours, according to witnesses.
They said many army vehicles carrying troops were deploying in the centre of Khartoum early Thursday.
The group spearheading the nationwide demonstrations urged residents of the capital and elsewhere to mass outside army headquarters.
"We call on our people from across the Khartoum capital and the region around to immediately go to the sit-in area and not leave from there until our next statement is issued," the Sudanese Professionals Association said.
Death toll mounts
The wider alliance the SPA has formed with opposition parties and some rebel groups from Sudan's war-torn regions said the sit-in would continue until Bashir steps down and makes way for sweeping reforms.
"We have to continue to gather at the sit-in area until the conditions of our revolution as agreed by our alliance have been met," the Alliance for Freedom and Change said.
The demonstrators have braved repeated volleys of tear gas from members of the powerful National Intelligence and Security Service (NISS) since they began camping outside the complex on April 6, protest organisers say.
But for the first time on Tuesday night they did not face any "threat" from security agents, said a protester who requested anonymity for security reasons.
That came after 11 people, including six members of the security forces, were killed on Tuesday during demonstrations in the capital, government spokesman Hassan Ismail told the official SUNA news agency.
Officials say 49 people have died in protest-related violence since demonstrations first erupted in December.
"I hope our revolution will achieve its goal," said Alaa Salah, dubbed the protest movement's "Nubian queen", after a video clip went viral of her conducting chants with demonstrators outside the army headquarters.
Earlier this week, the US, Britain and Norway for the first time threw their weight behind the protesters.
"The Sudanese authorities must now respond and deliver a credible plan for this political transition," the countries' Khartoum embassies said in a statement.
Sudan, along with Iran, Syria and North Korea, is on Washington's blacklist of state sponsors of terrorism.
Bashir, who is wanted by the International Criminal Court on charges of war crimes and genocide, came to power in a 1989 coup. He is one of Africa's longest-serving presidents.
On Tuesday, security agents had to abort attempts to disperse the crowds when soldiers countered their volleys of tear gas by firing in the air, witnesses said.
NISS said it was "monitoring the demonstrations and discharging its duty according to law".
Sudan's police has ordered its forces not to intervene against protesters.
"We call on God to preserve the security and calm of our country... and to unite the Sudanese people... for an agreement which would support the peaceful transition of power," it said in a statement.
On Wednesday, protesters were raising funds to ensure a regular supply of food and water for the crowd.
"Many shop owners and businessmen have offered us free supplies," said one demonstrator.
Protesters have set up five big screens at the complex to screen football matches, an onlooker said.
Witnesses said troops stationed vehicles mounted with machine-guns at the gates of the complex.
The SPA said "several members and leaders" of Sudan's paramilitary Rapid Support Force (RSF) had given indications they would join the movement.
The RSF is made up of Arab militias that fought on the side of government forces against rebels in Sudan's western region of Darfur in the initial years of the conflict.
Bashir's ruling National Congress Party said plans to hold a rally backing the president on Thursday had been postponed.