Filed at 9:58 a.m. ET

JUBA, Sudan (Reuters) - Khartoum is arming militias, as well as civilians in south Sudan, in order to destabilize the tribally fractured semi-autonomous region, officials from the leading southern party have said.

The international community has been increasingly worried about fighting between southern tribes that has claimed at least 950 lives this year, mostly women and children, in bloody attacks on entire villages by heavily armed tribal groups.

Khartoum's National Congress Party (NCP) and the former southern rebel group, the Sudan People's Liberation Movement (SPLM), signed a peace deal in 2005 that ended more than 20 years of vicious north-south war.

The south was given a share in national oil revenues as well as its own government, headed by the former rebels that also took seats in the national parliament.

"Yes they are arming, even as the Government of Southern Sudan (GOSS) has disarmed civilians," SPLM Spokesman Yien Matthew said on Saturday.

"The National Congress (Party) has been arming militia groups to cause instability in south Sudan...(and) has also been arming civilians," Pagan Amum, Secretary General of the SPLM told journalists on Thursday in the southern capital Juba.

Speaking after a high-level SPLM meeting, Amum said that the party had laid out a plan to stop the movement of guns into the south that included monitoring of the north-south border and continuing civilian disarmament.

Inter-tribal fighting, often over cattle, takes place annually but the south's President Salva Kiir has blamed the recent intensification on unnamed agitators that he said were trying to show that the south is unable to govern itself ahead of the 2011 referendum.

The worst of this year's tribal fighting took place in the south's Jonglei State between the Murle and Lou Nuer tribes. Yien said that the SPLM believed Khartoum may have had a hand in this, but did not give details.

Speaking more generally, Matthew said guns bearing a logo of a Khartoum manufacturer had been found in the south.

Guns proliferated amongst southern communities during the 22 year north-south war, which saw tribal groups pitted against each other in some of the bloodiest fighting. Some tribal militias were supported by Khartoum.

Amum said that the NCP was also arming civilians "all over" northern Sudan, including in the western Darfur region where a six-year-old war continues.

"This is very dangerous plan to cause the collapse and instability all over the country and we call on the National Congress to review this policy, to stop it," Amum said.

He called for Sudan- wide disarmament and the strengthening

of law enforcement agencies.

Amum's statements came one day after the SPLM and NCP signed a new agreement promising to hasten the demarcation of the contentious north-south border, as well as seeking to resolve other sticking points in the north-south deal.

North and south Sudan's civil war was fought mainly over differing political ideologies and religious and ethnic identities, and claimed more than 2 million lives. It is separate from the conflict in Darfur.

Relations between the NCP and the SPLM have been rough since the 2005 accord, which is looking especially fragile in the face of elections planned for April and a southern referendum on secession from the north, set for 2011.

Many southerners say they would like to be part of a separate country.

(Reporting by Skye Wheeler, additional reporting by Jose Vieira)