By Aaron Maasho
ADDIS ABABA (Reuters) - South Sudan's rebels have demanded that Uganda stop supporting government forces as a condition for signing a ceasefire to end fighting that has riven Africa's youngest nation, a spokesman said on Thursday.
The president of neighboring Uganda, Yoweri Museveni, admitted for the first time on Wednesday that he was helping South Sudanese President Salva Kiir to fight the rebel forces.
Ugandan officials had previously denied taking any part in combat, insisting their troops were evacuating stranded Ugandans and helping protect the airport and the presidential palace in South Sudan's capital Juba.
Kampala's military involvement has annoyed Ethiopia, which is hosting peace talks, and raised worries that it could expand a conflict that, according to one independent estimate, may have killed up to 10,000 people since it erupted in mid-December.
Peace talks aimed at ending the fighting between Kiir's forces and supporters of Riek Machar, who was sacked as vice president in July, are being sponsored by the regional African body IGAD in the Ethiopian capital Addis Ababa.
"IGAD has our complaint. The foreign troops have complicated the conflict so I think it's also a matter of common sense for them to withdraw," said Mabior Garang, a spokesman for Machar's delegation attending the Addis Ababa talks.
"These are sticking points that the government does not want to move away from," he said.
A member of Kiir's delegation, who declined to be named, said: "We have a military pact with Uganda. The status of our cooperation should only be discussed among the two governments, not with a rebel group."
The two sides' delegations have so far made no obvious sign of progress towards a ceasefire deal.
The Kiir government has previously rejected rebel demands that 11 detained politicians allied to Machar be released before a ceasefire is signed. Juba insists they must be investigated.
The rebels have since said that freeing detainees is not a precondition for a ceasefire. They are now focusing on Uganda's role and have also demanded the end of a state of emergency imposed by Kiir on the strategic regions of Jonglei state and the oil producing states of Upper Nile and Unity.
Uganda backed the SPLA, now led by Kiir, during the south's years of war with the Sudanese government in Khartoum. South Sudan declared independence in 2011, after a 2005 peace deal with Khartoum.
Machar has accused Uganda of staging air strikes against his supporters.
Uganda's Museveni has threatened Machar with defeat if he does not accept a ceasefire.
He has also said Machar should withdraw "to a remote area of the country to avoid attack and to start talks unconditionally so as to resolve the problem quickly".
(Editing by Edmund Blair and Gareth Jones)