JUBA South Sudan said on Monday Sudanese war planes bombed an oil region in the newly independent state, a day after Khartoum declared a state of emergency in some border areas as tensions showed no signs of abating.
Weeks of border fighting have raised fears Sudan and South Sudan could return to all-out war, after failing to resolve a string of disputes over oil revenues and border demarcation.
Philip Aguer, spokesman for South Sudan's army, the SPLA, said Sudanese forces had bombed Panakuach in Unity State.
"There was bombing in Panakuach yesterday. Not less than four bombs were dropped," Aguer said, adding there had been no reports of casualties.
There was no immediate comment from the Sudanese army.
South Sudan has accused Sudan of using its warplanes to bomb its territories. Khartoum has denied it, though it has said it reserves the right to use air strikes in self-defense.
Unity State has come under repeated bombardment over the past week, and an air strike in its capital Bentiu last Monday killed two people.
Sudanese President Omar Hassan al-Bashir on Sunday declared a state of emergency in some areas of South Kordofan, White Nile and Sinnar provinces bordering South Sudan.
Meanwhile, Foreign Minister Ali Ahmed Karti said Sudan reserved the right to deploy its forces along the border with South Sudan for legitimate protection.
"This is within the borders of Sudan and not outside of Sudan and this is our right, we can deploy our forces anywhere," he said in Moscow after meeting his Russian counterpart.
"We're not at all preparing ourselves for war."
The former civil war foes also accuse each other of backing rebel militias. Each side denies the other's allegations.
The spokesman for the Sudan People's Liberation Movement-North (SPLM-N), a rebel group that has been fighting the Sudanese army in South Kordofan and Blue Nile states since last year, said the group had taken control of the town of Talodi.
He said SPLM-N fighters had pushed out Sudanese forces from the town after government forces killed three civilians in two separate bombings in other areas, but Khartoum's army spokesman al-Sawarmi Khalid denied those accounts.
"The military forces did wide combing of the area outside Talodi and succeeded in pushing backing SPLM-N forces," he told Reuters by telephone, saying that was away from Talodi itself.
"There are no clashes inside Talodi and it is under full government control. Any talk of SPLM forces being in Talodi is mere lies," Khalid said. "The army did not bomb any civilians."
Further raising tensions was Sudan's arrest of a Briton, Norwegian and South African who it said had illegally entered the disputed Heglig area to spy for the SPLA.
South Sudanese officials have denied these allegations and said the men had been working with United Nations and aid groups clearing mines and had got lost in the remote territory.
The U.N. mission in South Sudan (UMISS) which said one of its officials had been taken to Khartoum with the three other men, was trying to free the group.
"UNMISS has been in contact with the Sudanese authorities to try and secure their release," said Josephine Guerrero, a spokeswoman for the mission.
The Sudanese foreign ministry said it had held discussions with the ambassadors of the countries of those arrested. In a statement, it said it told the ambassadors that the three were being investigated because they entered Sudan illegally.
"They were in areas of military activity, they possessed military equipment," the statement said, adding that the detainees were being treated in accordance with the standards of international law and the investigation would be speedy.
South Sudan seceded from Sudan in July, six months after a referendum agreed under a 2005 peace deal that ended two decades of civil war which killed more than 2 million people.
But distrust runs deep between the neighbors, who are at loggerheads over the position of their border, how much the landlocked south should pay to transport its oil through Sudan, the division of national debt and other issues.
The African Union is pushing to bring both sides to the table, giving them an ultimatum of three months to reach a deal. South Sudan has said it accepts the African Union's seven-point plan, which calls for an immediate cessation of hostilities.
The African Union said in a statement on Monday it looked forward to receiving Sudan's formal acceptance of the road map so that steps can be taken towards implementing it.
Russia said on Monday a draft U.N. Security Council resolution on Sudan and South Sudan did not amount to a threat of sanctions but that "economic measures" could be taken against the two countries if they failed to comply with calls to stop hostilities.
(Additional reporting by Khaled Abelaziz and Ulf Laessing in Khartoum and Lidia Kelly in Moscow; Writing by Dina Zayed in Cairo; Editing by Andrew Roche)