Constant gunfire and explosions early yesterday were followed by a few hours of relative calm before sporadic gunfire resumed.
At least 26 people have been killed in the clashes in the capital, health ministry undersecretary Makur Matur Kariom said.
Speaking from Juba Teaching Hospital, he added: "These are the people we received at the hospital and who died actually at the hospital. Whoever died outside the hospital, we don't have their numbers."
Mr Kiir imposed a dusk-to-dawn curfew on Monday in a bid to restore order. Residents say the security clampdown makes life that was already tough even harder.
One aid worker in Juba, who asked not to be named, said: "Food and water is an issue as people don't have fridges or power so they buy food almost daily. They haven't stocked up and are getting worried."