JUBA, Sudan, March 31 (Reuters) - Ugandan gunmen killed some 20 south Sudanese, kidnapped others and stole thousands of cattle in a cross-border raid on a remote area in early March, southern Sudanese officials said on Monday.

Officials in the area blamed the attack on the UPDF (Ugandan People's Defence Force), "but the Ugandan authorities said no, it might be (Ugandan) game wardens," South Sudanwese Vice President Riek Machar told Reuters.

The semi-autonomous southern administration is investigating the attack but details remain unclear, he said, adding that cross-border and inter-tribal attacks were common where south Sudan shares a porous border with Uganda, Kenya and Ethiopia.

Machar is the chief mediator in peace talks between the Ugandan government and the Ugandan rebel Lord's Resistance Army (LRA), which have agreed to sign a peace deal next week after almost two years of negotiations.

Machar said that after the Ugandan accord had been signed, a conference was planned in south Sudan's capital Juba for all four countries to try to end the insecurity in the border region, devastated by civil war in south Sudan and north Uganda.

"We could do a simultaneous disarmament after sensitising the civilian population," Machar said. More than 20 years of civil conflict in Sudan ended in 2005 with a north-south peace accord, but many southern communities still have weapons.

Disarmament has proved difficult in the south as unarmed tribesmen fall prey to nomadic armed tribes who cross state and national borders.

Machar could not confirm the number killed in the raid but said it was around 20. "Some cattle were taken and also some citizens were taken across the border,"he said.

He said the violence was "not accepted" but added that he did not see the incident as likely to strain relations between the south and Uganda, which was an important ally for the southern rebels during the north-south conflict.

Napon, who blamed Kampala for the attack, said: "If the (Ugandan) government has a problem that our people entered their land, they should talk to us. Reporting by Skye Wheeler, Editing by Opheera McDoom and Tim Pearce)

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