Amnesty International estimates that from June 2011-April 2012, more than 114,000 people from Sudan fled to South Sudan while another 30,000 left for Ethiopia. Civilians along the border between Sudan and newly independent South Sudan are facing the worst of the crisis, the rights group said.
Border conflicts, ethnic turmoil and disputes over oil are threatening a peace deal that gave South Sudan its independence and ended one of the bloodiest civil wars in modern history.
Mark Toner, a spokesman for the State Department, said Washington was providing more than $34 million to support the emergency response for Sudanese refugees.
"The United States is concerned about the dire situation faced by the growing Sudanese refugee population in South Sudan," he said in a statement.
"We remain deeply committed to meeting the humanitarian needs of the people of South Sudan, and urge the international community to join us in our efforts to relieve suffering and assist those affected by the on-going violence."
Amnesty International said the Sudanese military was to blame for much of the crisis.