Juba (AFP) - Rebels in South Sudan have launched a large-scale attack on the strategic northern oil hub and state capital of Malakal, an official and aid sources said Saturday.
Fierce fighting was reported to be raging inside the city, situated in the country's oil-rich north, in what appeared to be a major counter-attack against a weeks-old offensive by government troops.
"The rebels of Riek Machar have attacked Malakal from all directions, from east, west, north and south, and the fighting up to now is continuing," Information Minister Michael Makuei told AFP.
He said government troops had so far "managed to repulse the rebels" to keep them from capturing the city, the capital of the Upper Nile State.
It was left in ruins last year after repeatedly swapping hands since South Sudan's civil war broke out in December 2013, when President Salva Kiir accused his sacked deputy Machar of attempting a coup.
The country has since been carved up along ethnic lines, divided between Kiir's Dinka tribe and Machar's Nuer tribe, as well as several other ethnic militia groups.
Analysts and aid workers believe tens of thousands of people have been killed in the fighting in the world's youngest nation, which only gained independence from Sudan in 2011.
Officials said the attack began just before darkness on Friday, with rebels crossing the White Nile river on boats -- apparently aided by a local militia commander from the ethnic Shilluk people who had been a pro-government general.
The commander, Johnson Olony, is a powerful military figure in the key oil-producing state of Upper Nile. He has also been accused of abducting scores of children to fight in his force.
"It was Olony who transported the rebels across the river bank to Malakal," Makuei said.
- 'Appalling' abuses -
Aid workers in the city who spoke to AFP reported intense gunfire as well as the thump of heavy explosions from artillery or mortar fire.
On Friday a report by the regional bloc pushing peace efforts accused South Sudan's army of carrying out "grave" human rights abuses in their all-out offensive.
East Africa's eight-country IGAD bloc -- whose peace initiative collapsed in March -- condemned the "unwarranted and appalling actions" of the government, reporting "violence targeting civilians, grave human rights abuses and destruction of villages."
The assault, which began in late April, is one of the heaviest government offensives in the 17-month long civil war, with gunmen raping, torching towns and looting aid supplies in the northern battleground state of Unity, according to the UN and aid agencies.
The UN's aid chief in South Sudan, Toby Lanzer, this week said the number of civilians left without "life-saving aid" due to the offensive in Unity alone had risen to 500,000, after the UN and aid agencies pulled out due to a surge in fighting.
Over half of the country's 12 million people are in need of aid, with 2.5 million people facing severe food insecurity, according to the UN.
Well over 117,000 civilians are sheltering in UN bases across the country.