(Adds Sudan army comment, details from rebel report)
* Sudan army says repulsed attack, denies rebel claim
* South Sudan seceded from the north on July 9
* Analysts say south's secession could embolden rebels
KHARTOUM, July 19 (Reuters) - The most powerful rebel group in Sudan's western Darfur region said it successfully attacked a government position alongside other anti-Khartoum fighters in an oil state bordering South Sudan.
Sudan's army dismissed the statement.
While the report from the Justice and Equality Movement (JEM) could not be independently confirmed, it suggested an attempt at closer coordination between various rebel groups left in the north after the south seceded on July 9.
Senior JEM official Al-Tahir al-Feki said the group attacked a government garrison in Southern Kordofan on July 10 -- a day after the south seceded -- in a joint operation with the northern branch of the Sudan People's Liberation Army (SPLA).
The operation ended on the night of July 17, he added.
"We managed to take a substantial number of RPGs (rocket propelled grenades) and AK-47s," Feki said by phone. "We will conduct further operations combining JEM and the SPLA northern sector."
Sudan's army said in a statement the military had repulsed the rebel attack south of Southern Kordofan's capital Kadugli and dismissed JEM's statement that it assisted in the assault.
"The presence of JEM forces in Southern Kordofan is a media presence only," said the statement published by the Sudanese Media Centre, a news agency linked to Sudan's state security apparatus.
South Sudan formally seceded from Sudan on July 9 under a 2005 peace deal that ended decades of civil war with the north, but many fighters who sided with the SPLA against Khartoum remained on the northern side of the new border.
Fighting between southern-aligned fighters and government troops broke out on June 5 in Southern Kordofan -- which borders South Sudan, Darfur and the disputed Abyei region -- and has gradually escalated to include artillery and aircraft.
Aid workers say a humanitarian crisis may emerge in the region. A draft U.N. report said the Sudanese army's alleged actions there could amount to war crimes.
Khartoum rejects the charges, saying it is fighting to ensure stability and help civilians.
A separate insurgency has raged in Darfur since 2003. While down from its peak, a surge in violence since December has forced tens of thousands of people to flee their homes.
Analysts have said the south's secession could embolden rebel movements in the north.
Some 2 million people died in the north-south civil war, waged for all but a few years since 1955 over religion, ideology, ethnicity and oil.
An estimated 300,000 people have died in the Darfur conflict in the west, the United Nations says. Khartoum puts the toll at 10,000.
Sudan signed a peace accord with a small Darfur rebel group on Thursday, but JEM and other larger groups have refused to participate or dropped out of the talks. (Reporting by Alex Dziadosz; editing by Maria Golovnina)
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