A satellite monitoring group has reported that Sudan's military is upgrading its air bases in its Blue Nile state. This could be an indication of possible air strikes in the region along the country's border with South Sudan.

This report has come in the wake of United Nations officials having accused the Sudanese government of bombing the Yida camp in the South Sudanese state of Unity. Navi Pillay, the UN Human Rights Chief, has called for an investigation into the incident.

If indeed it is established that an international crime or serious human rights violation has been committed, then those responsible should be brought to justice, she said.

We are extremely concerned about the more than 20,000 refugees who have sought safety in Yida,'' said Lise Grande, the UN humanitarian co-ordinator in Juba. South Sudanese officials said that at least 12 people were killed in the attack on Yida.

Sudan's armed forces, however, denied they carried out the strike.

This information is completely false. We didn't bomb any camps or any areas inside the borders of South Sudan, said Sawarmi Khaled Saad, the spokesman for the Sudan Armed Forces (SAF), to the AFP news agency. He added that Khartoum had no interest in destabilizing South Sudan.

The Satellite Sentinel Project said it captured images that appeared to show active enhancement of two air bases. These helipads will allow the SAF to base helicopter gunships and transport helicopters needed for the transport of air assault infantry near the border with South Sudan, said the Sentinel report.

The government of Sudan submitted a complaint this month to the UN Security Council, alleging that South Sudan is backing rebels in the border states of Blue Nile and Southern Kordofan.

After voting overwhelmingly for secession in a January referendum, South Sudan split off into a separate country in July.