S.Sudan denies rumours of president Salva Kiir's death as tensions rise

South Sudan's government was on Wednesday forced to deny President Salva Kiir had died, following days of rumours over his health that have heightened tensions in the capital Juba.

"This is a mere lie, there is nothing as such, Salva Kiir has not even been sick," Information Minister Michael Makuei Lueth told journalists in Juba, slamming "wild rumours" he said aimed to divide the people of South Sudan.

The rumours have been doing the rounds on Twitter, and even spread as far as Uganda where Kiir, 65, was reported to have fled for medical treatment.

Residents of Juba reported a higher than usual presence of soldiers on the streets, as the rumours coincided with mounting concerns over an uptick in violence in the troubled nation in recent weeks.

"We are scared of the situation. You cannot know what is exactly happening but (there are) rumours that the president has died. Well, it is said fighting may break out and this is why I am scared," said Moses Modi, a resident of Juba who was staying home over security fears.

Another Juba resident, speaking on condition of anonymity, reported that some schools had sent pupils back home.

"There are soldiers deployed along the road. Mainly the roads around the ministries and the State House ... I am at work but leaving (for) home now. Because the tension is high," she added.

South Sudan, which gained independence in July 2011, descended into war just two and a half years later when Kiir in December 2013 accused his former deputy Riek Machar of plotting a coup.

Numerous attempts to shore up a fragile truce failed, and in a major setback to peace efforts, fierce clashes erupted in Juba on July 8 this year between Kiir's guards and troops loyal to Machar.

The international community has expressed deep concerns over a spread in violence since the July clashes, which pushed the number of refugees from the war-scarred nation past the one-million mark, according to the UNHCR.

In a further blow to peace hopes, Machar last month urged "a popular armed resistance" against his rival's government.

Machar, who fled to Khartoum in the July fighting, on Wednesday left for South Africa for medical tests.

The United Nations Mission in South Sudan (UNMISS) on Wednesday said it was "extremely concerned over increased reports of violence and armed conflict in various parts of the country in the last few weeks."

In the town of Leer, in the north, UNMISS forces reported heavy artillery and gunfire exchanges between forces loyal to Kiir and Machar, leading to an unspecified number of deaths and sending local populations fleeing.

In a statement UNMISS said it had been denied access to an area where some 21 civilians were reportedly killed in an ambush on the road between Juba and the southern city of Yei over the weekend.