South Sudan rebel leader Gatluak Gai was shot dead in Unity state on Saturday, the army and a rebel source said, just a week after agreeing to a ceasefire and as the newly independent country renewed its amnesty offer. It was unclear how Gai was killed, with the SPLA, the army of the south, insisting he was shot 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," army spokesman Philip Aguer told AFP. South Sudan, which declared independence from the north on July 9, faces a host of truly daunting challenges. Among the greatest of these is the threat posed by at least seven militia groups within its borders, with more than 1,800 people killed in violent conflict so far this year, 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 rebel leader changed his mind three days ago, which led to a split within the militia, Aguer added. "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. But a spokesman for another rebel group active in Unity state, which borders the north, contradicted Aguer'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," Bol Gatkouth told AFP by phone. "It was a way of luring him in so that they could catch him," he added