A vessel loaded with some 600,000 barrels of crude oil produced in South Sudan stands idle at a Sudanese port, blocked over the refusal of the government in Juba to pay customs fees.

South Sudan captured 75 percent of Sudanese oil when it came independent early last month. But since it is landlocked, it must rely on Sudan's export terminal on the Red Sea. Refineries also only exist in the north.

South Sudan's government recently accused Khartoum of waging economic war by charging transit and custom fees that amount to what it called “daylight robbery.”

The two nations are engaged in negotiations on sharing oil revenues. But the dispute over customs fees is further escalating tensions and could disrupt the export of oil from one of Africa's largest producers.