More than 35,000 Sudanese refugees have recently fled into neighboring South Sudan to escape fighting, officials said.

More than 35,000 refugees from Sudan's southern Blue Nile state have sought asylum in South Sudan in the past three weeks, U.N. High Commissioner for Refugees spokesman Andrej Mahecic said.

Fighting erupted in Sudan's South Kordofan state in June 2011 and spread to Blue Nile state three months later.

Refugees are fleeing both aerial attacks and increased fighting between units of the Sudanese armed forces battling Sudan People's Liberation Army (North) insurgent guerrilla forces, along with growing food shortages resulting from the clashes.

Since December, UNHCR has been sending emergency supplies to South Sudan by both air and road, the agency said Tuesday.

The influx of refugees threatens to overwhelm UNHCR efforts however, as South Sudan, one of the world's poorest states, is now hosting roughly 150,000 refugees from Sudan.

South Sudan doesn't have the resources to cope with the sudden influx of refugees.

"This is a dramatic change in an already difficult humanitarian situation," U.N. High Commissioner for Refugees Antonio Guterre said. "Not only are refugee numbers suddenly much higher, but the condition that many of these people are in is shockingly bad. Some have been eating tree leaves to survive along the way."

South Sudan officially seceded from Khartoum July 9, 2011, after an internationally supervised vote, becoming an independent state and severing Africa's largest country in two following a 2005 peace treaty that ended nearly five decades of conflict between the mostly Muslim north and heavily Christian south.

South Sudan took with it 75 percent of the Sudan's known oil reserves, even as export pipelines remained under Sudan's control and the two countries have spent the last 11 months wrangling over the terms under which South Sudan could utilize Sudan's pipeline network for export.

The month that South Sudan achieved independence, Sudanese Minister of Finance and National Economy Ali Mahmood Hassanein told the National Assembly that 73 percent of the country's oil was in the former south, 26 percent in the north and 1 percent in the contested Abyei region.

While the 2005 Comprehensive Peace Agreement stated that northern and southern Sudan would equally split the revenue from oil exports, financial arrangements remain unresolved. Aside from pricing disputes, South Sudan is claiming that Khartoum is arming South Sudanese rebel groups in order to destabilize the new country and retake control of its oil fields.

China depends on the two Sudans for about 5 percent of its oil, buying about 365,000 barrels per day of the former Sudanese unitary state's 500,000 bpd production. In the first 10 months of 2011, despite the political fracturing of the state, China's imports of Sudanese crude were up 5.5 percent on the same period a year before, reaching 11.1 million tons.