Sudan's President Omar al-Bashir has arrived in Juba for talks with South Sudanese President Salva Kiir over the conflict in South Sudan, reports say.
Separately, the two warring parties in South Sudan have begun direct talks in Ethiopia aiming at a ceasefire. No substantive progress has yet been made.
The conflict pits supporters of Mr Kiir against rebels led by his sacked deputy, Riek Machar.
At least 1,000 people have been killed since violence erupted on 15 December.
The unrest started after Mr Kiir accused Mr Machar of attempting a coup - which he denies.
Nearly 200,000 people have been displaced in the conflict, which has taken on ethnic undertones. Mr Kiir is from the majority Dinka community and Mr Machar from the Nuer group.
Mr Bashir says his visit to the South Sudanese capital Juba with a team of ministers is aimed at giving support for a regional initiative to solve the crisis.
"There should be peace and security in South Sudan," Mr Bashir said as he arrived in Juba.
"We come so that we can bring peace to South Sudan, to our brothers and sisters in South Sudan. Our relationship is very important," Mr Bashir said, according to AFP.
Sudan relies on revenue from oil transported through its southern neighbours' pipelines, which Khartoum fears will be disrupted by the fighting.
Meanwhile, East Africa's regional bloc the Intergovernmental Authority on Development (Igad) is trying to mediate between the South Sudanese government and its opponents at the talks in Ethiopia's capital, Addis Ababa.
China's Foreign Minister Wang Yi is also due to hold talks with the warring parties, in an attempt to push them to agree to a cessation of hostilities.
China is a major investor in South Sudan's oil industry.
Rebel negotiator Mabior Garang said he was optimistic about talks with the government, the AFP news agency reports.
However, he was "suspicious of the sincerity of the government" as it kept "shifting the goal posts", he said.
Up until Friday, the talks were conducted by mediators. Now, teams representing the opposing factions in South Sudan are expected to negotiate face to face.
Key issues are establishing a ceasefire, and the rebels' demand for the release of what they see as political prisoners.
Heavy fighting is continuing to the south of Bor, one of two cities held by rebels, says the BBC's Alastair Leithead, who was on the road between Juba and Bor.
The rebels include a former military division made up of thousands of men who switched sides, our correspondent says.
Until a ceasefire is agreed, fighting is expected to continue or even intensify, he adds.
On Sunday, a South Sudanese army general was killed when a government convoy was ambushed.
South Sudan is the world's newest state. It was formed in 2011, gaining independence from Sudan after decades of conflict.
The latest trouble has its roots in tensions that go back long before 2011.