JUBA South Sudan on Friday accused Sudan of killing seven people in air strikes on a disputed area and said its northern neighbor was jeopardizing a plan to restart cross-border oil flows by massing troops along their joint border.
Sudan has already denied the accusations of bombing - which South Sudan said lasted for three days - and a Sudanese military spokesman was not immediately available on Friday to respond to the new troop movement allegation.
The African neighbors agreed to end hostilities in September and to resume oil exports from the South via the north after coming close to war in April, the worst outbreak of violence since South Sudan's secession last year.
But tensions flared up again this week after the two countries accused one another of failing to move their forces back from the unmarked joint border, something both had said must happen before oil exports could resume.
Philip Aguer, a spokesman for South Sudan's army, said Sudanese Antonov warplanes had dropped 27 bombs on Kiir Adem, an area lying inside a 14 mile-wide strip of land claimed by both countries since Tuesday.
"As a result of this aggression seven people died ... these are all civilians," Aguer said, saying that eight people had been wounded. "They are militarizing the border instead of demilitarizing it."
Khartoum denied the bombing accusations on Wednesday, saying its forces had instead attacked a camp of rebels from the Darfur region "deep inside its territory".
But the rebels denied they had been bombed.
"Every time Khartoum bombs civilians they announce they are bombing rebel groups. That is not correct. They didn't bomb us," Abu Al-Gassim Immam, a spokesman for the rebel Sudan Revolutionary Front said by telephone.
The front is an alliance of rebels from Darfur and the Sudanese states of South Kordofan and Blue Nile on the other side of the joint border that is battling to topple Sudan's President Omar Hassan al-Bashir.
Sudan and South Sudan accuse one another of supporting rebels on each other's territory, something both deny. Analysts regard such allegations as credible however.
South Sudan seceded in July last year after overwhelmingly voting for independence in a referendum promised in a 2005 peace deal that ended a civil war.
In April, the two nations clashed on another part of their poorly-defined border, the Heglig oilfield, but pulled back from the brink of war after international pressure.
In September, the rival Sudans agreed to recognize administrative borders used by former colonial power Britain at independence in 1956 and to pull their armies back 10 km (6 miles). However, the exact position of this line is disputed.
Mile 14 runs parallel to the south bank of the River Kiir, known as Bahr al Arab in the north. The waterway formed a natural boundary between the southern Dinka Malual tribe and the northern Rizeigat tribe.
Britain moved the border southwards to allow the Rizeigat grazing rights south of the river in the early 20th century. The United Nations mission in South Sudan says Kiir Adem lies north of the 1956 border and south of the Kiir river.
(Reporting by Hereward Holland; Editing by Ulf Laessing and Andrew Osborn)