JUBA (Reuters) - South Sudanese rebels have kidnapped eight locals working for a U.S. charity and are demanding aid deliveries as ransom, a military spokesman said on Monday, as food in the famine-hit nation looks increasingly likely to become a weapon of war.

The aid workers were taken from a village near Mayendit, about 420 miles (680 km) northeast of the capital of Juba, Brigadier General Lul Ruai Koang told Reuters.

“The rebels attacked and abducted eight local staff from Samaritan’s Purse and they are being held to ransom. They have demanded that the organization takes aid to them,” he said.

The charity confirmed the kidnapping in a statement but denied a ransom had been demanded.

“We have been in contact with them and they have not been harmed. No ransom request has been made and we are hopeful that they will be released soon and safely,” it said.

Last week, South Sudan announced plans to charge a levy of $10,000 per foreign aid worker, which with the danger of abduction, could hurt efforts to help the hungry.

Nicholas Haysom, U.N. Special Envoy to Sudan and South Sudan, said: “It is ... likely to lead to an exodus of humanitarian workers in a country that is already facing a dire humanitarian situation.

“It also makes what is happening even more opaque ... using food aid as a weapon of war, by either side.”

Oil-rich South Sudan, the world’s youngest nation, has been mired in civil war since President Salva Kiir, an ethnic Dinka, sacked his deputy Riek Machar, a Nuer, in 2013.

The fighting has forced 3 million people to flee their homes, split much of the country along ethnic lines and paralyzed agriculture, prompting the U.N. to declare last month that parts of the country are suffering from famine.

Citizens of the cash-strapped country have also been hit by hyperinflation that topped 800 percent last year. The government’s efforts to rebuild the shattered economy have been hampered by rebel attacks on oil facilities.

Two Indian employees of the Ministry of Petroleum were kidnapped on March 8 in northeast Maiwut state, and Minister of Petroleum Ezekiel Lol Gatluak, blaming the rebels, said: “We are working to make sure that they are unconditionally released.”

Also in the north, clashes between the army and rebels killed at least 23 people and injured 56 on Sunday, Koang said, with the insurgents attacking government positions, looting and setting fire to houses in the oil-rich Bieh state.

“They attacked our position on Sunday. Our forces fought back in self defense and managed to repulse the attackers,” he said.

A rebel spokesman was not immediately available for comment.