South Sudan is warning that it may stop exporting oil through Sudan's pipelines again.

An official in South Sudan's oil ministry told The Associated Press that Sudan has blocked the export of South Sudanese oil. The official insisted he not be identified because he is not authorized to release the information.

While speaking at a police graduation ceremony in Juba on Monday, South Sudan President Salva Kiir warned there could be oil shutdown like the one that ended nearly two months ago. He said Juba was still working with Sudan "in a diplomatic way."

South Sudan resumed oil production in April this year, 16 months after a shutdown caused by disagreements with Sudan over oil transit fees.