JUBA South Sudan said on Wednesday that Sudanese warplanes had bombed its territory, killing one civilian and wounding four others, a fresh setback to plans to resume cross-border oil flows.
Sudan and South Sudan agreed in September to end hostilities and restart vital southern oil exports through Sudan after coming close to war in April, the worst violence since the south became independent in July 2011.
But relations have soured again in the past few days after both sides failed to agree on how to move their forces back from the unmarked joint border, something both had said must happen before oil exports resume.
South Sudan's army said Sudanese warplanes had bombed its side of the border, the first such accusation since the September deal.
"Sudan bombed our people in Northern Bahr al Ghazal. The bombing happened yesterday at 2 p.m.," army spokesman Philip Aguer said. "We were caught by surprise."
There was no immediate comment from Sudan, which has previously denied bombing the South although Reuters has witnessed several air strikes.
Sudan says rebels fighting the Khartoum government operate from south of the border, something analysts find credible despite denials from Juba.
Any delay to a resumption of the oil trade would be a serious blow to both countries.
Sudan benefits from South Sudan's oil exports because Juba has to pay a fee for using northern pipelines and a Red Sea port. Juba halted production in January because of disputes over pipeline fees with Sudan.
South Sudan's President Salva Kiir said on Tuesday the resumption of oil production had been delayed after Sudan had made further demands.
Concerns about delays to reopening the oil pipeline pushed the Sudanese pound to a historic low at the start of the week, highlighting the need to restart oil flows, a vital source of state revenues and dollars for both countries.
Analysts say while both governments need the oil they also want to be seen as tough on the other side to shore up domestic support.
(Reporting by Charlton Doki in Juba; Writing by Ulf Laessing; Editing by Robin Pomeroy)