* S. Sudan struggles to assert authority in vast area
* Rebellion started last year following election loss
More than 150 people have been killed in a battle between South Sudan's army and insurgents in the eastern Jonglei state, officials said on Thursday.
The African country's army earlier this month launched an offensive against rebels led by David Yau Yau in Jonglei where the government hopes to search for oil with the help of France's Total.
Since winning independence from Sudan in July 2011, South Sudan has been struggling to impose its authority across vast swathes of territory bristling with weapons after decades of civil war with Khartoum.
Yau Yau mounted a rebellion last year, with support from his Murle ethnic group, after losing local elections in 2010.
Army spokesman Philip Aguer told Reuters his forces had killed 143 fighters from Yau Yau's militia in a battle east of Pibor town on Tuesday. Twenty soldiers were killed and 70 people were wounded, he said.
Information Minister Barnaba Marial Benjamin said the army, or SPLA, had seized an air strip which had been used to drop ammunition and arms to Yau Yau's troops.
"The SPLA is moving in the area so as to put an end to the rebellion," he said.
South Sudan has accused arch rival Sudan of supporting Yau Yau and other rebel groups, a claim denied by Khartoum.
A shortwave radio station with links to the Yau Yau rebellion says the group is fighting the government in reaction to abuses committed during a state disarmament programme in Jonglei.
Rights groups accuse South Sudan's army of human rights violations during a disarmament push aimed at ending a cycle of clashes between the Murle and Lou Nuer tribes.
Nearly 900 people died when about 7,000 armed youths of the Lou Nuer tribe attacked Murle villages in the Pibor area at the end of last year, according to the United Nations.