South Sudan is ready to resume negotiations with Sudan, Juba's lead negotiator said late Tuesday on the eve of a United Nations date to restart talks, but also accused Khartoum of not being willing to meet.

"As per the timeline set out in the UN Security Council resolution, the parties are supposed to have resumed negotiations by the 16th of May, and we have not received any invite," negotiator Pagan Amum told AFP.

He said Juba has sent a letter to the African Union mediator, former South African president Thabo Mbeki, saying "we have been ready to resume talks and we are waiting".

"South Sudan has committed to implementing the roadmap and UNSC Resolution 2046 and we have started to take the steps required. We withdrew our forces from Abyei just like we did from Heglig and we announced the cessation of hostilities" to the AU, he said.

But Amum said that Sudan has not reciprocated and the AU has not enforced a two-week deadline for negotiations to restart by Wednesday.

"I believe it is because the government of Sudan hasn't been keen to return to talks, which is in violation of the UNSC resolution and the AU roadmap" adopted on April 24 and confirmed by the UN resolution, he said.

While South Sudan announced this week that it had finished pulling its police officers from the contested region of Abyei, Sudanese troops that have occupied it since last May have remained.

"The government of Sudan is continuing to violate the resolution. They have not withdrawn from Abyei and they did not declare a cessation of hostilities" or stopped them, he said.

The UN gave both sides a May 5 deadline to cease hostilities after a month of vicious fighting between the two armies and rebel groups on the largely undefined border.

But South Sudan has said that aerial bombardment and ground attacks by SAF and Khartoum-backed militias have continued, while Sudan says the South has not stopped funding rebels along its border that it has been fighting for months.

"The UN must consider to take actions against the Republic of Sudan for the bombings, ground attacks and refusal to get out of Abyei", Amum said, adding he did not know why Khartoum was stalling the talks.