As residents of Juba prepared a send-off for Garang on Saturday, two planeloads of Sudanese soldiers, including members of the elite presidential guard, landed at Juba airport on Friday and were immediately deployed around town.
Soldiers armed with rocket-propelled grenade launchers and assault rifles were positioned at 10-metre intervals on the streets of Juba, which was rocked by deadly violence after Garang's death, an AFP correspondent said.
Those soldiers joined fighters from Garang's ex-rebel Sudan People's Liberation Movement/Army (SPLM/A) who entered Juba for the first time on Wednesday to help quell the violence and provide security for the funeral.
Half a million people, including Sudanese President Omar al-Bashir, South African President Thabo Mbeki, Kenyan President Mwai Kibaki and Ugandan President Yoweri Museveni, are expected to attend the service.
Officials from the African Union and the United Nations were also expected.
Garang was killed on 30 July when his helicopter crashed in what Sudanese, Ugandan and SPLM/A officials repeatedly have said was an accident due to poor weather.
But on Friday, Museveni said it may not have been an accident, becoming the first official of any government to publicly suggest the crash may have been the result of foul play.
"Some people say accident. It may be an accident, it may be something else," Museveni told thousands of mourners in the southern Sudanese town of Yei where Garang's coffin had been taken in an airborne funeral procession to Juba.
Yoweri Museveni: Garang's death
may not have been an accident
"The [helicopter] was very well equipped. This was my [helicopter] the one I am flying all the time. I am not ruling anything out," he said, adding that an unspecified "external factor" could have been responsible.
Salva Kiir, Garang's successor as SPLM/A chief, declined to comment on the specifics of Museveni's remarks but said no cause had been ruled out pending an international investigation.
But in Khartoum and Juba, senior SPLM/A officials cautioned against making any assumptions about the cause of the crash as did a diplomat in Bor, Garang's birthplace, where his coffin was taken after Yei.
Call for cooperation
Sudanese Foreign Minister Mustafa Osman Ismail called on Uganda to cooperate with the investigation into the crash.
"[Garang's] visit was to Uganda and the aircraft and its crew were Ugandan," Ismail told the official SUNA news agency.
However, he expressed displeasure that the Ugandan authorities informed Sudan about the disappearance of Garang's helicopter several hours after they found out.
Garang died with 13 others
in a helicopter crash
Sudanese Information Minister Abdul Basit Sebdarat went further, calling Museveni's comments "extremely worrying".
"Uttering statements or speculations ahead of the investigation would harm the probe and the chances of finding the facts," SUNA quoted Sebdarat as saying.
Garang's death sparked violence between northerners and southerners in Khartoum and the south, and 130 were killed and hundreds wounded.
His death and the rioting have raised fears of the unravelling of the landmark January peace deal he signed with Khartoum that ended Sudan's 21-year civil war between the Muslim north and the mainly Christian and animist south.
Relative calm returned to the streets of Khartoum as Muslim leaders appealed for peace and shop-owners reopened for business.
As the Sudanese soldiers and SPLM/A fighters spread throughout Juba, thousands of volunteers descended on a former military training ground to help prepare Garang's burial site.
Up to 130 people died in riots
after Garang's death
Weeping women, stoic men and curious children converged on the site near the state parliament where construction was under way on a brick and mortar mausoleum to house Garang's remains.
In accordance with Dinka tribal tradition, one of Garang's sons, Chol, a 25-year-old fine arts student in Britain, dug up the first chunk of earth where his father will be laid to rest.
"It is a shock. It seems like a dream," he told reporters of his father's death.
"Sometimes I wake up and find people weeping," Chol said. "I never thought I would ever be digging my father's grave."