More than 120,000 people need humanitarian aid because of a wave of ethnic clashes in a remote and volatile region of South Sudan, the United Nations said Friday, underscoring the challenges the world's newest nation faces six months after independence.

The government of Sudan also reported clashes in a state bordering the new nation.

The battles in Jonglei state are straining international relief efforts, said Lise Grande, the U.N. Humanitarian Coordinator in South Sudan. The U.N. mission originally projected that the same number of people displaced in South Sudan in 2011 -- 350,000 -- would be displaced in 2012.

"We are two weeks into the year and there have already been 120,000 impacted," said Grande.

The U.N. earlier this month estimated that 60,000 people had been affected by clashes between the Lou Nuer and Murle communities. The Lou Nuer sent a column of at least 6,000 warriors to attack the Murle in late December and early January, sending tens of thousands of people fleeing into the countryside. The Murle have since carried out revenge attacks.

No reliable death toll has yet been established in the series of attacks. Government officials have estimated that over 160 have been killed in Murle revenge attacks. A county commissioner initially estimated more than 3,000 had been killed in the Lou Nuer attacks on Pibor, but the central government has cast doubt on that figure.

The U.N. is also trying to establish the number of dead. But more than two weeks after the end of the Pibor attacks, Grande said they have not come to any conclusions.

"Like everyone else we are waiting to see what is confirmed," said Grande.

U.N. officials in South Sudan are calling humanitarian operations in Jonglei state the most expensive and complex since the signing of the 2005 Comprehensive Peace Agreement, which ended more than 20 years of civil war between Sudan and South Sudan. South Sudan broke away from Sudan in July.

While U.N. humanitarian operations have reached communities in Pibor County, the displaced in Uror, Akobo and Duk counties must wait until the U.N. completes its humanitarian assessments.

Jonglei state is roughly the size of England but there are few roads and the majority of food aid must be flown in by helicopter. The instability in the state has led Russia to threaten to withdraw four helicopters it has provided to the U.N. mission.

South Sudan has deployed 3,000 security forces to the state to try and quell the waves of violence. The Sudan Council of Churches, which has been heavily involved in peace efforts, called the deployment "too little, too late."

Sudan's military said on its website Friday that seven opposition fighters from the Sudan People's Liberation Movement-North -- the military movement in Sudan that aligns itself with South Sudan -- were killed in clashes with Sudanese soldiers in the country's Blue Nile State, which borders South Sudan.

It is believed that anti-government rebels of the SPLA still control parts of the state. The clashes took place near the border with South Sudan earlier this week, military spokesman Sawarme Khalid Saad was quoted as saying.

Six soldiers were wounded in the clashes, which resulted in the military driving the rebels out of the area, Saad said. Late last year, the U.N. refugee agency said some 1,200 people were arriving daily from Sudan's Blue Nile State to South Sudan, and that around 350,000 people have moved from Sudan to South Sudan since independence in July.

The Sudanese government also denounced U.S. efforts to distribute humanitarian aid in South Kordofan and Blue Nile states because it excluded the participation of national humanitarian organizations. This could result in aid falling into the hands of opposition fighters, Humanitarian Aid Commissioner Suleiman Abdul Rahman Suleiman said.

He was quoted in the state-run SUNA news agency Friday calling on the U.S. to explain its motives for delivering humanitarian aid without the Sudanese government's participation in areas where the SPLM is active.