Khartoum - South Sudan's President Salva Kiir was in Khartoum for talks with his Sudanese counterpart on Tuesday after a new flare-up of fighting in his country's 11-month civil war.
Last week, rebels attacked the oil town of Bentiu, capital of Unity state on the Sudanese border, ending a lull in fighting during the rainy season, which renders roads impassable to military vehicles.
Clashes between the rebels and troops loyal to Kiir have also raged in neighbouring Upper Nile state, another key oil-producing area, further threatening the south's exports though Sudan, a key revenue earner for Khartoum.
Kiir was greeted at the airport by President Omar al-Bashir and other top officials on his first visit to Sudan since April, an AFP correspondent reported.
Southern oil exports through Port Sudan were high on the agenda for their talks, along with security issues and demarcation of the two countries' contested border, Sudan's ambassador to Juba said on Monday.
South Sudan split from the north in 2011 under a peace deal that ended a 22-year civil war. Its secession saw the South take most of the formerly united country's 470,000 barrels per day of oil production.
But the civil war, which erupted in the South last December, has seriously hit its oil output and Khartoum's earnings from transit fees on exports, which all pass through Sudan.
What began as a political dispute between Kiir and his former vice president Riek Machar has degenerated into a brutal ethnic conflict between their Dinka and Nuer peoples, driving 1.8 million people from their homes.
Hundreds of thousands have fled across the border to camps in Sudan.
The two governments remain at odds over a string of unresolved issues from the South's secession, including the contested border.
In 2012, the two countries briefly battled for control of the Heglig oil field on the frontier before Khartoum asserted its control over the area.
Sapa-AFP