A U.S. satellite monitoring group said Friday that Sudan's military is upgrading air bases near the border with South Sudan and building up air resources in what could be a precursor to a widened aerial bombing campaign.
The report came one day after officials accused Sudan of bombing a refugee camp in South Sudan, which became the world's newest country only four months ago. The government of Khartoum denied Friday that there was even a camp housing northern Sudanese refugees who fled south for refuge, adding that its air force had not bombed any area of South Sudan.
Four bombs fell in and around a camp called Yida in Unity State. No casualties were reported, though one bomb landed on the grounds of a school while 300 students were in class. That bomb did not detonate.
The U.N. refugee agency on Friday condemned the bombing of the camp, and the U.S. called the attack abhorrent and outrageous. The U.S. demanded that Sudan halt aerial bombardments immediately. Another bombing in a separate area of South Sudan earlier this week killed seven people, according to South Sudan President Salva Kiir.
The U.N. human rights chief, meanwhile, called for an investigation into Thursday's bombings. Navi Pillay said if it is established that an international crime or serious human rights violation occurred, then those responsible should face consequences.
"This latest attack risks aggravating what is already an extremely tense and dangerous situation," she said.
Kiir said Thursday he fears the Khartoum-based Sudanese government intends to invade the south soon.
Sudan's U.N. ambassador denied reports his country bombed areas of South Sudan, and the American ambassador says he's a liar.
Sudanese Ambassador Daffa-Alla Elhag Ali Osman told journalists after a Security Council meeting on the matter Friday that the reports were "fabrications" and "there was no aerial bombardment."
The United States' U.N. Ambassador Susan Rice told journalists that the reports of bombing by Sudan along its border with South Sudan have been confirmed by U.N. officials. She said the Sudanese envoy "blatantly lied" to council members.
The Satellite Sentinel Project said satellite imagery appears to show the enhancement of two air bases Sudan seized in Kurmuk from rebels in Sudan's Blue Nile State. The group says the images show three helicopter gunships and an Antonov, the plane witnesses said was used in Thursday's bombing run of the Yida refugee camp.
The violence near the new border between Sudan and South Sudan is especially troubling given the history between the two. The black African tribes of South Sudan and the mainly Arab north battled two civil wars over more than five decades, and some 2 million died in the latest war, from 1983-2005.
A peace deal ended the war and South Sudan became its own country in July after a successful independence referendum. But there have been lingering disputes over border demarcation, oil-sharing revenues and all-out warfare between Sudan's military or proxies and a military force inside Sudan that aligns itself politically and culturally with the south.
Sudan has accused the south of arming those groups, and taken that accusation to the U.N. Security Council. Kiir on Thursday denied that charge.
John Prendergast a Sudan activist and the co-founder of the Enough Project, said the airfield improvements suggest that Sudan will widen its aerial campaign in border areas of South Kordofan and Blue Nile in Sudan, as well as in South Sudan.
"If this buildup and bombing campaign isn't countered aggressively by the international community, it appears likely that Khartoum's actions will plunge Sudan even more deeply into internal war as well as ignite a full-scale war with South Sudan. This is threatening to explode into the largest conventional war on the face of the earth," Prendergast said.
Omer Ismail, a policy adviser for the Enough Project, said the indiscriminate bombings of refugees fleeing war is a "grave" violation of international humanitarian law.
In the buildup to South Sudan's January independence referendum and its July declaration as the world's newest country, the U.S. had indicated it would consider easing economic sanctions against Sudan if it would allow the south to break free without interference. But talk of normalizing relations has subsided as Sudan has continued military maneuvers along the border.
Twice this week the U.S. strongly condemned bombardments by Sudan against South Sudan, and it urged South Sudan to exercise restraint to prevent the further escalation of hostilities. The U.S. also called on Sudan and the Sudan People's Liberation Movement-North _ the military movement in Sudan that aligns itself with South Sudan _ to cease fighting and resume talks.
John Heilprin in Geneva and Mohammed Osman in Khartoum, Sudan, contributed to this report.
(This version corrects to U.S. instead of U.N. in 10th paragraph.)