The United States has strongly condemned an airstrike by Sudan on its southern neighbor that allegedly killed seven people.

South Sudan says Sudanese jet fighters bombed an area of Upper Nile state on Monday, near the two countries' border.

In a statement late Wednesday, the U.S. State Department described the attack as indiscriminate bombing of civilian targets and said it condemns the airstrike “in the strongest possible terms.”

It also called the attack provocative, and said such bombardments increase the chance of war between Sudan and South Sudan.

The two countries have been at sharp odds since the south split from Sudan in July, six years after the end of Sudan's long north-south civil war.

Sudan has accused the south of supporting rebels in two states along the border, Southern Kordofan and Blue Nile. The south has accused Khartoum of planning war on the south and whipping up unrest among southern militia groups.

Sudan has recognized the south's independence but the sides have yet to resolve issues over borders — especially in the oil-rich Abyei region — and the sharing of oil revenue. The south took over most of Sudan's oil in the split but pipelines to the sea run through the north.