* South says Sudan mounted two attacks on Wednesday
* No comment available from Khartoum
* South says on alert but won't retaliate
By Andrew Green
JUBA, July 5 (Reuters) - South Sudan accused Sudan's army on Friday of launching two separate attacks with planes and land troops on areas near their disputed border, in a new sign of friction between the former civil war foes.
Relations between the African neighbours hit a low when Sudan threatened last month to halt South Sudanese oil exports passing through the north unless Juba cut ties with rebels operating across the shared border. South Sudan denies any such links.
Both sides had agreed in March to set up a border buffer zone and resume cross-border oil flows in a bid to end hostilities after coming close to war in April 2012, in the worst violence since the South seceded two years ago.
The African Union is trying to defuse the oil showdown but mistrust remains deep between the neighbours, which fought one of Africa's oldest civil wars between 1983 and 2005.
South Sudan's army spokesman Philip Aguer said two Sudanese MiG warplanes had bombed military positions in the disputed Jau area on Wednesday, wounding four soldiers and two civilians.
He said Sudanese infantry troops had earlier that day pushed into Southern territory north of the Nile port of Renk in Upper Nile state, apparently to try to seize fertile land. South Sudan's army had repulsed the attack, Aguer added.
"This is a complete violation of all the agreements, mainly the security arrangements and the creation of a buffer zone," he said.
Sudan's military spokesman al-Sawarmi Khalid could not be immediately reached on Friday, a holiday in Sudan. Khartoum categorically denies attacking South Sudan but Reuters reporters have witnessed some attacks in the past.
Aguer said South Sudan was not planning a counter-attack. "Our soldiers are on maximum alert to be on self-defence, but will not react to these provocations," he said.
Much of the almost 2,000 km (1,300 mile) border is disputed. Jau is a particular hot spot because Khartoum believes rebels use the area to cross the unmarked boundary to stage attacks inside Sudan and retreat afterwards into the South.
In September, the rival Sudans agreed to recognise 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.
Sudan has said it will close the two cross-border pipelines by August unless support for rebels stops. But analysts doubt it will happen because Sudan needs pipeline fees from the South to stabilise its battered economy. (Writing by Ulf Laessing; Editing by Mark Trevelyan)
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