Nestle's Nespresso brand said it had halted coffee operations for now in South Sudan, where opposition leader Riek Machar has called for a return to war against the government.

"We had to temporarily suspend our operations in the country. It is the third time this happened since we started working there," Nespresso spokeswoman Jacquelyn Campo said on Tuesday, confirming a report in the Wall Street Journal (WSJ).

"The situation has deteriorated and is very difficult at the moment," she said, adding it was impossible to say at this stage when the company would be able to resume business there.

The premium coffee brand started working with local farmers in South Sudan in 2011, in partnership with non-profit organisation TechnoServe, to revive coffee production which had been destroyed by years of armed conflict in the region.

It launched a first limited-edition Robusta coffee from South Sudan one year ago.

South Sudan split from Sudan in 2011 after decades of civil war fuelled by ethnic divides and disputes over oil, but internal conflicts and political power struggles have persisted, with fresh clashes flaring in July.

Campo said Nespresso had invested over $2.5 million in the project and had so far trained 731 South Sudanese coffee farmers. Its partner, TechnoServe, will launch a radio programme to remotely train coffee farmers at the end of this month, she said.