U.N. Secretary-General Ban Ki-moon has called on Sudan and South Sudan to “disengage” and return to negotiations after recent reports of fighting along their border.

Speaking to the U.N. General Assembly in New York Wednesday, Mr. Ban said another element in consolidating peace between the two countries is for each to address internal issues.

“The Government of Sudan must address legitimate political and economic aspirations of its people in Southern Kordofan and Blue Nile where humanitarian access should be immediately granted and a cessation of hostilities negotiated. The Government of South Sudan must address grievances behind inter-communal violence and gain the full trust of its population. It is imperative that both sides stop any and all warfare by proxy, before it become too late.”

He noted that Wednesday was the deadline for the two sides to establish a Joint Border Verification Monitoring Mechanism, as part of a U.N. Security Council resolution adopted last week.

The resolution also called on Sudan and South Sudan to cease hostilities or face possible sanctions.

South Sudan on Wednesday accused Sudan of carrying out days of cross-border airstrikes.

Rising tensions have pushed the countries to the brink of war, just 10 months after South Sudan formally split from the north.

The countries have yet to resolve critical issues from their split, including citizenship questions and disputes over oil revenue and borders.

The two sides have accepted “in principle” an African Union roadmap, which calls for the Sudans to settle their disputes in 90 days or face binding international arbitration.

Fighting has displaced tens of thousands of people along the two countries' border area, creating a humanitarian crisis that aid agencies say is rapidly growing worse.

U.N. human rights chief Navi Pillay is on a five-day trip to South Sudan to meet with leaders and discuss the protection of civilians.