The newly independent nation of South Sudan says the government in Khartoum is engaging in “economic war” by issuing a new currency and by imposing oil transit fees that it says amount to “daylight robbery.”

Those accusations Monday by Pagan Amum, the secretary-general of the south's ruling party came less than three weeks after the nation of Sudan split in two. He called charging nearly $23 per barrel to transport oil through Sudan's pipelines a “hostile act.”

South Sudan now controls most oil production, which has been a major source of Sudanese revenue. But in order to export that oil, South Sudan must use pipelines that run though Sudan's territory.

Speaking to reporters in South Sudan's capital, Juba, Amum said the Sudanese government violated an agreement when on Sunday it debuted its new pound. Many South Sudanese continue to hold the old Sudanese currency, and there is concern those pounds will no longer be honored.

South Sudan introduced its own currency, also called the pound, less than a week ago.

The two countries are still at odds over several major issues, including borders, the future of the disputed Abyei region, and how to share oil revenue.

A special U.S. envoy has embarked on a mission that will take him to both Khartoum and Juba to urge the leaders of both nations to restart negotiations on those issues that remain from the 2005 agreement ending Sudan's civil war.

According to a State Department statement, Princeton Lyman is to press for an immediate end to conflict and “unfettered humanitarian access” to the Southern Kordofan region of Sudan.

The envoy also will travel to Addis Ababa for talks with former South African President Thabo Mbeki and Ethiopian officials on the ongoing deployment of peacekeepers in the Abyei region.