A rebel group in South Sudan threatened on Saturday to attack remote Warrap state to bring down the local government and called on the United Nations and residents to leave within three days.

The South Sudan Liberation Army (SSLA) said it would turn its attention to Warrap state after earlier attacking Mayom town in neighbouring Unity state, also on the border of Sudan.

Within few days, the people of Warrap will be liberated from abject poverty, corruption and abuse of human rights, it said in a statement.

We would also advise the civilians to evacuate all towns and move to villages in order to be safe, it said.

There was no reaction from the United Nations which runs large humanitarian operations and food deliveries in South Sudan.

South Sudan became independent in July after a 2005 peace deal with Khartoum that ended decades of civil war, but the new nation has been struggling to end tribal and rebel violence that has killed around 3,000 people this year.

Several militias are fighting the army in remote parts of the country.

Officials in South Sudan said earlier on Saturday the SSLA had killed 15 people, including nine soldiers, and wounded 18 when attacking Mayom in the morning. The town lies in the west of Unity state bordering Warrap state.

We got attacked in Mayom town today by the militias from 6 to 7 a.m. The militia attacked the town, killed 15 and wounded 18, Unity state Information Minister Gideon Gatpan Thoar said. More than 60 militiamen were killed.

Army spokesman Philip Aguer said: It was indiscriminate, they didn't differentiate between civilians and the army. The killing included a doctor.

Aguer said Mayom was now under army control but the SSLA rejected that, adding in its statement: Within four hours, SSLA forces also managed to capture Tomor town and they are now advancing towards Bentiu town.

Analysts say the SSLA is a loose umbrella of militias with no clear political agenda. In a statement on Friday, the SSLA accused the Unity state government of human rights abuses and confiscating cattle.

South Sudan officials accuse Khartoum of supporting militias but the north denies this, and many rebels say they are fighting against what they see as corruption and ethnic discrimination in the south's government, charges Juba denies.

President Salva Kiir has had little success with several amnesty offers to rebels. Violence in remote parts of the African country is hard to verify as a lack of infrastructure makes access difficult for journalists and aid agencies.

(Reporting by Hereward Holland; Writing by Ulf Laessing)