Efforts to broker a ceasefire in South Sudan have continued with a US special envoy and other mediators meeting the rebel leader, Riek Machar.
Special envoy Donald Booth met Mr Machar at an undisclosed location in South Sudan.
He said later mediators would continue to press for the release of jailed associates of Mr Machar for them to attend peace talks in Ethiopia.
A rebel spokesman said a ceasefire would be signed if they were freed.
Speaking to BBC News, spokesman Hussein Mar Nyuot dismissed claims from the South Sudanese government that its forces were now in full control of Unity State.
He also described as baseless a government allegation that forces loyal to Mr Machar had damaged oil facilities there.
In another development, South Sudan's Oil Minister, Stephen Dhieu Dau, visited Khartoum to discuss the impact of the conflict on the oil industry with his Sudanese counterpart, Makawi Mohammed Awad.
South Sudan seceded from Sudan in 2011 after a long and bloody conflict, to become the world's newest state.
Most of the oilfields are in the South but the pipelines run through Sudan and oil is a crucial source of revenue for both countries.
The UN Security Council has urged South Sudan President Salva Kiir to release the political prisoners.
However, Mr Machar's forces appear on the back foot after losing the town of Bentiu, the capital of oil-rich Unity State, to government forces on Friday.
The government says it is mobilising thousands of troops to retake Bor - the last major town controlled by Mr Machar's forces.
The conflict began on 15 December between forces loyal to the president and forces loyal to Mr Machar, his former vice-president.
According to the UN, the fighting has killed "very substantially in excess" of 1,000 people.