(CNN) -- The president of Sudan declared a state of emergency Sunday for cities along the hotly contested border with South Sudan, where Sudanese fighter jets launched at least one attack against their neighbor's ground forces.
Sudanese President Omar al-Bashir said the state of emergency covers cities in the provinces of South Kordofan, White Nile, and Sinnar, which are on the eastern half of its border with South Sudan.
A journalist in South Sudan's Unity state, just over the border from South Kordofan, reported coming under attack by Sudanese helicopter gunships and MiG fighter jets Sunday morning.
Robyn Kriel said she was traveling to the front line with the Sudan People's Liberation Army of South Sudan when they came under heavy fire for 15 minutes. They all took cover in trenches dug by the army, she told CNN.
The SPLA was poorly equipped for the fight, she reported. Soldiers used anti-aircraft missiles and even hand-held weapons that they fired in the air, she said.
At least four SPLA soldiers were hurt in the attack, she said.
The South Sudanese military reported another attack on Unity state Saturday, though a Sudanese military spokesman denied it was involved.
South Sudan split from Sudan last year as part of a 2005 peace deal that ended decades of war in Africa's largest nation. The war left 2 million people dead and ended with the peace agreement that included an independence referendum for the south.
Significant issues between the countries remain unresolved, however, including status of their citizens, division of national debt, disputed border areas and sharing of oil wealth.
Tensions peaked this month when South Sudan seized the oil-producing region of Heglig, a resource that fuels the economies of both nations, from its northern neighbor. Heglig oil facilities account for about half of Sudan's production of 115,000 barrels a day.
South Sudanese forces withdrew days later after Sudan lodged protests with the United Nations and African Union, but South Sudan said it continued to come under aerial and ground attack.