Sudan and South Sudan agreed on Wednesday to reactivate a joint monitoring force along their contested border, a source said, as the southern government fights a rebellion.
The decision came during a meeting between South Sudan's defence minister, Kuol Manyang Juuk, and his Sudanese counterpart Abdelrahim Mohammed Hussein.
Juuk arrived in Khartoum on Tuesday for an official visit. Later on Wednesday he presented President Omar al-Bashir with a letter from the South's leader, Salva Kiir. Its message was not revealed.
"In two weeks' time they will reactivate" the UN-supported Joint Border Verification and Monitoring Mechanism as well as other forums for coordinating security between the countries, which fought border clashes in 2012, said the source who declined to be identified but is familiar with the ministers' decision.
The mechanism was set up last year to monitor a buffer zone 10 kilometres (6.2 miles) on each side of a 1956 border line.
All activities of the monitoring unit were suspended after South Sudan's government decided in November to temporarily withdraw its monitors in a dispute over the buffer zone centreline, UN chief Ban Ki-moon said in a February report.
Sudan and South Sudan disagree over certain parts of their border, which has not been demarcated.
Three weeks after the South pulled out of the mechanism, a clash between troops loyal to Kiir and those backing sacked vice president Riek Machar led to full-scale fighting in South Sudan.
Almost one million civilians have been displaced, including more than 40,000 who have arrived in Sudan, according to the United Nations.
Kiir's forces now control much of the South's Unity state, but Upper Nile remains a "patchwork of zones of control", according to the Small Arms Survey, a Swiss-based independent research project.
Both states produce the oil which is vital to Khartoum and Juba.
The South separated in July 2011 under a peace agreement that ended a 1983-2005 civil war.
But tensions remained until Kiir and Bashir held a summit in September last year, confirming their commitment to nine security and economic cooperation pacts. These included the demilitarised buffer zone.
Relations were improving, but then war broke out in the South, diverting the two governments from putting all nine deals into effect.
The defence ministers "agreed to activate implementation of the cooperation agreements", Sudan's official SUNA news agency said after Wednesday's talks.
Western governments have commended Sudan's role in supporting regional efforts to bring peace to South Sudan.