Sudanese President Omar al-Bashir met last week with South Sudanese President Salva Kiir. Bashir's visit to the South Sudanese capital was his first since South Sudan gained independence in 2011.
Border security, disputes over oil and ethnic conflicts have threatened to unravel the peace deal that secured South Sudan's independence. A deal brokered in Ethiopia last year outlined a path to peace that includes border security and other obligations.
Ban said in a statement he was encouraged by Bashir's visit, adding that both sides need "to maintain this positive momentum."
U.N. peacekeepers last month verified that both sides had pulled military forces from border areas and worked to establish a demilitarized zone.
South Sudan's security has been challenged by ongoing fighting in Jonglei, its largest state. Five members of a U.N. peacekeeping mission in South Sudan, known by its initials UNMISS, were killed while on patrol there last week.
The attack in Jonglei follows a report from the United Nations investigating violence that killed at least 85 people in the state in early 2013 when unnamed gangs attacked cattle herders.