The authorities are investigating but early reports suggest bad weather and poor visibility may be to blame.
There are fears South Sudan may be plunged back into a civil war less than a decade after it ended.
Both government and opposition groups have been accused of being responsible for the deadly attack.
The disruption in oil supplies has caused shortages and concerns in several African countries.
Some 50,000 people are told to flee their homes as the army warns of a huge military offensive in Jonglei state.
Medical aid groups have described the scale of casualties as alarming as people seek treatment.
The political rift that could spiral into conflict again after the vice-president was accused of treason.
MSF says a government air strike hit its hospital after another of its health facilities was looted.
The appointment of a dead opposition politician to a presidential panel caused embarrassment.
