Women who fled a war across the border in Sudan's Blue Nile state sit outside a clinic in Doro refugee camp. Sudan is fighting a civil war on multiple fronts in Darfur, South Kordofan and Blue Nile, with almost 100,000 fleeing across the border into the newly-independent South Sudan. (Hereward Holland /Reuters)

Renewed cross-border clashes between Sudan and the new nation of South Sudan are raising fears of a worsening humanitarian crisis, with some officials warning that the violence is reminiscent of the conflict in Darfur.

Hundreds of people have fled Sudan in recent days, heading to camps in South Sudan and western Ethi­o­pia where tens of thousands have sought refuge since the crisis began last year, U.N. officials say.

“The refugees are crossing into South Sudan from Sudan’s troubled Blue Nile state,” Fatoumata Lejeune-Kaba, a spokeswoman for the U.N. High Commissioner for Refugees, told reporters in Geneva. “They say they fled because of bombardments and the fear of more violence.”

South Sudan, which celebrated independence in July, has been besieged by numerous conflicts, including ethnic and tribal fights and a bitter dispute with its former rulers in Khartoum over oil fees.

In the South Kordofan region, once a major battleground during Sudan’s 22-year civil war, fighting broke out in June between Sudanese forces and rebels formerly allied with the Sudan People’s Liberation Movement. By September, the conflict had spread to Blue Nile state.

This past week, Mukesh Kapila, a former U.N. representative to Sudan and now a human rights activist, said the conditions in South Kordofan could become as violent as they had been in a separate conflict in Darfur, a vast region in western Sudan. That conflict pitted the Arab-ruled government in Khartoum against non-Arab rebels. According to the United Nations, more than 300,000 died and 2.7 million were displaced, prompting the United States to declare that a genocide had taken place.

Kapila, who had recently returned from a visit to the Nuba Mountains in South Kordofan, told reporters in Nairobi that Sudanese airplanes routinely bomb civilians, actions he deemed “tantamount to war crimes.”

“Inside the Nuba Mountains, I saw burnt villages, destroyed food stores and damaged schools and churches used by civilians to shelter from the fighting,” said Kapila, now with the Aegis Trust, a human rights group that campaigns against genocide.

“I heard an Antonov [airplane] myself and watched women and children running away, shrieking with fear, as well as fields on fire from dropped bombs destroying what little food crops were being planted,” Kapila said.

Sudan has denied the allegations, but it has also prevented foreign relief agencies from entering the Nuba Mountains, even as U.N. and other aid groups report food shortages and malnutrition.

The conflict appears to be intensifying. Sudanese airplanes allegedly bombed border areas in late February and again this month. In November, bombs hit the Yida refugee camp near the border, and U.N. officials are concerned it will be struck again.

“We are extremely concerned about the safety of people in the nearby Yida refugee settlement, which hosts 16,022 Sudanese,” Lejeune-Kaba said.

U.S. Rep. Frank R. Wolf (R-Va.), who recently visited Yida, said in a statement this week: “In speaking with the refugees in the camp, I heard echoes of Darfur — accounts of ethnic cleansing, mass murder and rape of innocent civilians in the region. As any Sudan watcher knows, this is familiar ground for Sudanese President Omar Bashir — an internationally indicted war criminal.”

Wolf, along with two other members of Congress, Reps. Jim McGovern (D-Mass.) and Michael E. Capuano (D-Mass.), this past week introduced the Sudan Peace, Security and Accountability Act, which calls for tough actions against Bashir and an end to human rights violations in the Nuba Mountains.

One recommendation said that “no American tax dollars should be going to countries that welcome Bashir.”

The U.N. Security Council also weighed in this past week, calling for a cease-fire “to put an end to the cycle of violence.” The Obama administration welcomed the council’s action.

“The United States remains deeply concerned about the grave humanitarian situation in Southern Kordofan and Blue Nile, where hundreds of thousands endure the daily threat of violence and looming famine without an urgent infusion of life-saving assistance,” said Susan Rice, the U.S. ambassador to the United Nations.