* One of several South Sudan rebel leaders killed
* Africa's newest nation hit by rebel and tribal violence
(Adds details, background)
By Jeremy Clarke
JUBA, July 23 (Reuters) - A south Sudanese rebel leader was killed on Saturday, the southern army and a separate rebel group said, as the new nation's rulers try to quell the violence that threatens their push for much-needed stability.
South Sudan seceded from the north on July 9 -- a separation won in a January referendum that was the climax of a 2005 peace deal ending decades of civil war with Khartoum.
The oil-producing state is struggling with poverty, underdevelopment and persistent instability that threatens its east African neighbours.
At least seven rebel militias are fighting the new government's forces in remote parts of a country roughly the size of France.
Gatluak Gai, one of several militia commanders in the south, was shot dead by his own group in oil-producing Unity state after agreeing a ceasefire with the government, said Philip Aguer, spokesman for the southern army known as SPLA.
"Gatluak Gai was killed by his deputy. It was an internal division. He (had) signed a peace (deal) with the SPLA," he said.
Aguer said Gai had changed his mind about his militia being integrated into the SPLA after agreeing to it earlier this week. The shooting began after an argument with his officers, he said.
"Gatluak Gai and three others were killed in the shooting," Aguer said.
A separate rebel group headed by former southern army officer Peter Gadet, which is also active in Unity state, said the SPLA had killed Gai. "Gatluak Gai has been killed by the SPLA. They shot him," spokesman Gatkuoth Kol said.
Sudan watchers say Gai was not one of the top rebel leaders and was less powerful than Gadet or George Athor, another militia commander.
South Sudanese President Salva Kiir has renewed an offer of amnesty to armed groups fighting his government, but previous pardons have had little success.
Kol said rebels led by Gadet and Athor will reject the amnesty offer after Gai's killing.
"We will not talk to the South Sudan government after this ... This offer of amnesty they talk about and which is always in the media, this is what they do (if you accept it)," he said.
South Sudan has accused Khartoum of supporting militias but the north denies this, and many rebels say they are fighting against what they see as corruption and ethnic discrimination in the south's government, charges it denies.
More than 2,300 people have been killed in rebel and tribal violence in the south in 2011, according to the United Nations. (Reporting by Jeremy Clarke, writing by Ulf Laessing, editing by Tim Pearce)
Our Standards: The Thomson Reuters Trust Principles.
