The African Union said Wednesday it was "deeply alarmed" by worsening violence between Sudan and South Sudan and called for the withdrawal of Southern troops from the Heglig battle zone.

"The African Union expresses grave concern at the escalating armed conflict on the border between Sudan and South Sudan and calls upon both parties to exercise utmost restraint," it said in a statement.

South Sudan's parliament speaker urged lawmakers Wednesday to mobilize the people to defend the fledgling nation in case of all-out attack by Sudan, as battle raged along their contested border.

"Khartoum might be meaning a real war... If you don't defend yourself you will be finished, so you should go and mobilize the people on (the) ground to be ready," Speaker James Wani Igga told parliament.

Senior officials from Sudan and South Sudan met Monday for the first face-to-face talks since heavy fighting between their armies broke out last week in disputed oil-rich border regions.

As senior envoys met in Ethiopia, U.S. President Barack Obama called U.S.-backed South Sudan President Salva Kiir to urge restraint.

Crisis talks between Sudan and South Sudan were stalled Sunday as the two nations traded accusations over responsibility for recent clashes.

"We are here ... to attempt to make peace; the Government of Sudan is waging war on South Sudan," Juba's chief negotiator Pagan Amum told journalists.

Malawi's cabinet will decide if Sudan's President Omar al-Bashir can attend the AU summit in July, despite the war crimes warrant against him, the foreign minister told a weekly Saturday.

"This is a big decision and the whole government machinery needs to sit down to decide whether to allow, deny entry or arrest al-Bashir if he comes again," Foreign Minister Peter Mutharika told the Nation newspaper.

Sudanese warplanes bombed oil rich border regions of South Sudan overnight after days of clashes, but fighting on the ground between the rival armies has ceased, a Southern official said Wednesday.

"The ground assaults this morning have stopped but they (Sudan) have still been bombing us in the night," said Gideon Gatpan, information minister for the South's Unity state, the scene of the attack.

U.S. Secretary of State Hillary Clinton said Tuesday that fighting on Sudan's border with South Sudan was "deeply distressing" and that Khartoum bore the brunt of the blame for the violence.

"The weight of responsibility rests with Khartoum," Clinton told reporters, citing aerial bombing runs by the Sudanese government as "evidence of disproportionate force."

South Sudan will not return to war with Khartoum despite a second day of airstrikes and bloody ground assaults in contested border areas between the rival states, a Southern minister said Tuesday.

"As our president (Salva Kiir) has said, we cannot be dragged into a senseless war, but we will be in position to protect our territory and integrity," South Sudan's Information Minister Barnaba Marial Benjamin told reporters.

Sudanese warplanes launched a second day of bombardment of oil-rich areas of South Sudan, after bloody clashes between ground troops of the rival states, a Southern government official said Tuesday.

"After a day of attacks by air and ground troops on Monday, this morning we heard the Antonov (aircraft) return, and dropped two bombs," said Gideon Gatpan, information minister for South Sudan's Unity state.

Sudanese aircraft and ground troops attacked multiple positions in South Sudan's oil rich border regions Monday, sparking fierce battles and prompting Southern President Salva Kiir to warn of war.

"This morning the (Sudanese) airforce came and bombed... areas in Unity state," Kiir said at the opening of a ruling party meeting in the southern capital Juba.