Khartoum - Silence has followed Sudan's announcement four days ago that it had begun a counter-attack towards the oil centre of Heglig seized by Southern troops.
The military has released virtually no information about the situation on the ground.
"We don't know what happens" in the field, a foreign diplomat said.
"We are in a war of statements."
The army spokesperson remained unreachable by telephone for a third day on Tuesday, and has not given a press briefing since Saturday when he said his forces were kilometres from Heglig town seized on April 10 by the South.
Announcing the fight-back a day earlier the spokesperson, Sawarmi Khaled Saad, said Sudanese forces were "close" to Heglig and there was combat.
El Shafie Mohammed El Makki, head of political science at the University of Khartoum, said only the military knows the situation but they may now be preparing "to fight a severe war" because South Sudan said it would not pull out of the north's most important oil field.
"You have to know one thing," Makki said of the Sudanese. "They will fight until they get rid of them. They will not stop."
Many in Khartoum are asking how the South was able to take over the area so easily in the first place.
Sudan does not allow journalists to report independently in South Kordofan state to which Heglig belongs, making verification of the military situation difficult.
South Sudan's army vowed on Tuesday to hold their positions in Heglig, despite air strikes.
"If they advance, definitely SPLA is ready to fight back and repulse them... the SPLA is ready for them outside Heglig," Southern army spokesperson Philip Aguer told reporters in the South.
Nineteen South Sudanese soldiers have been killed since last Tuesday, while 240 Sudanese troops have lost their lives, Juba's army said previously, in figures impossible to verify.
Sudan has made no comment about casualties but an AFP photographer saw almost 100 wounded soldiers last weekend at a military hospital in Khartoum.
The Sudanese military is already facing a major insurgency in South Kordofan state, a smaller uprising in Blue Nile, and ongoing unrest in the Darfur region.
Both Sudan and South Sudan last week ordered mass mobilisations.
"Those who willingly want to go, they will train them and take them," Makki said. "They are not going to force people to go."
A relief convoy of trucks loaded with biscuits, other supplies, and students heading to the front to fight, set out on Tuesday from Khartoum's University of Science and Technology.
The fighting is the worst since South Sudan won independence last July after a 22-year civil war that ended in 2005, and has heightened nationalist feeling in the north.
Clashes broke out last month in the Heglig area but escalated last week with waves of aerial bombardment hitting the South and Juba's seizure of Heglig.
Although South Sudan disputes that Heglig belongs to Sudan, the area is not among the roughly 20% of the border officially contested.
Khartoum has denied launching a wave of air raids on Southern border areas, killing several civilians and hitting a UN peacekeeping camp on Monday.
United Nations chief Ban Ki-moon on Tuesday called on both sides to immediately stop fighting "and to respect international humanitarian law and the protection of civilians".
He was speaking in Luxembourg, where he called on Khartoum to stop bombing South Sudanese territory and for the South to leave Heglig immediately.