Sudan has also been massing ground forces in a nearby town, he said.
Al-Obeid Merwah, a spokesman for the Sudanese Foreign Ministry, did not return calls seeking comment.
South Sudan became independent from Sudan in July, but many issues remain unresolved, including the demarcation of the border and the sharing of oil revenue.
Separately, the International Criminal Court issued an arrest warrant for Sudan’s defense minister, the third senior government official sought by the court over alleged involvement in atrocities in the Darfur region of western Sudan.
The court said it wants Abdelrahim Mohamed Hussein arrested on a warrant containing seven counts of crimes against humanity and six war crimes, including murder, persecution, rape and torture. The charges cover 41 incidents, the court said.
Prosecutor Luis Moreno-Ocampo asked judges for the warrant in December, saying Hussein is among those who “bear greatest criminal responsibility” for atrocities in Darfur from August 2003 to March 2004.
Sudan does not recognize the court and refuses to hand over suspects, including President Omar Hassan al-Bashir, who is accused of genocide in Darfur. His government in Khartoum had denounced Moreno-Ocampo’s request for a warrant for Hussein.
At the time covered by the charges, Hussein was interior minister and the Sudanese government’s special representative in Darfur. He is accused of overseeing a state-sponsored plan to attack villages in western Darfur.
Sudan’s government is accused of unleashing Arab militias on civilians — a charge the government denies. The United Nations estimates that 300,000 people have died and 2.7 million have been displaced in the conflict.