According to the statement from the South Sudan negotiating team, Sudan has refused to export southern oil until the border security arrangements are fully implemented. This includes the deployment of more than 800 Ethiopian security forces along the border to monitor the agreement.
Sudan has also frequently accused South Sudan of supporting rebels in Sudan's South Kordofan and Blue Nile states. The rebel groups were part of South Sudan's army during its 21-year civil war with Khartoum. But since the South's independence it maintains it has cut off support for the rebel groups. Khartoum has insisted Juba must stop supporting the rebels before border security arrangements can be implemented. South Sudan however says Khartoum is trying to delay the negotiations by "imposing new conditions" not in previous agreements.
It is unclear when the two sides might meet again to break the nearly four months of deadlock. But according to South Sudan's negotiating team, any chance of implementing the September agreement "will require greater cooperation from Sudan."