South Sudan rebel leader Gatluak Gai was shot dead on Saturday, the army and rebels said, just a week after he agreed to a ceasefire and as the newly independent country renewed an amnesty offer. There were differing accounts of how Gai was killed, with the south\'s army the SPLA insisting he was gunned down by his own men after reneging on the agreement, and a rebel source saying he was \"murdered\" by the SPLA. \"He was not killed by the SPLA; he was killed by his own men\" in Unity state, army spokesman Philip Aguer told AFP by phone from Juba. South Sudan, which declared independence from the north on July 9, faces a host of daunting challenges. Among the greatest is the threat posed by at least seven militias within its borders, with more than 1,800 people killed in conflict so far this year, according to the United Nations, many between the army and the rebels in states across the country. Aguer said Gai, a renegade militia commander who rejected an amnesty offer from the southern government last year, signed a ceasefire last week after months of negotiations with Unity state Governor Taban Deng Gai. But the reconciliation had not been formalised and the rebel leader changed his mind three days ago, Aguer added, which led to a split within the militia. \"When he came back to the meeting with his men, some of them said they would not join him. Gatluak Gai and three others who fought with him were killed in the shooting that took place in the Bentiu area this morning. \"The 80 rebels that fought against them have agreed to join the SPLA,\" the army spokesman said. Gai\'s decision not to join the army, which had offered him the rank of Lieutenant General, and his death shortly afterwards, were \"a very big disappointment,\" Aguer added. But the spokesman for another rebel group active in Unity state, which borders the north, contradicted the army\'s account of what happened. \"Gatluak Gai was killed by the SPLA... He signed a peace agreement and was ambushed by the same forces he signed the agreement with. He was murdered,\" Bol Gatkouth told AFP. \"It was a way of luring him in so that they could catch him,\" said Gatkouth, speaking on behalf of the militia group headed by rebel leader Peter Gadet. In his inaugural speech as president of the world\'s newest nation, on July 9, Salva Kiir renewed his offer of an amnesty for all the southern rebel groups that he first made at an all-party political conference in Juba last year. Gatkouth said his group would not accept the amnesty because recent events, including the detention of Gabriel Tang, another rebel leader who surrendered in April, demonstrated the government was not serious about peace. \"The army is violating the amnesty, so we do not accept it... If it was a real amnesty, Gabriel Tang would be out of prison and Gatluak Gai would not have been killed,\" he said. Peter Gadet, a former southern general turned militia commander, and George Athor, another renegade southern general whose forces are active in Jonglei state, are considered the two most powerful rebel leaders in South Sudan. Juba has traditionally accused Khartoum of supporting the different southern rebel groups in a bid to destabilise the country, as it did during the devastating 1983-2005 civil war, claims rejected by the north. Aguer said both the main rebel leaders were currently on the border with the north, which he suggested was responsible for persuading the rebels to abandon the reconciliation process. \"It seems some of the commanders in the north are trying to change their minds,\" he said.