UNITED NATIONS -- The situation in South Sudan's Jonglei state remains tense, said deputy UN spokesman Eduardo del Buey here Wednesday, quoting a report by the Office for the Coordination of Humanitarian Affairs (OCHA).

"Civilians continue to be affected by inter-communal clashes and fighting between the South Sudan army and armed groups," del Buey said at a daily news briefing here.

"Although the full scope of displacement in the state is unclear due to insecurity and limited access to many areas, aid organizations have reported that almost all of the estimated 9,000 inhabitants of the town of Pibor have left their homes," he said. "Tens of thousands of people are thought to have been displaced by recent clashes."

According to del Buey, UN agencies and their humanitarian partners are planning an assessment of the affected communities' needs, in a bid to reach more displaced people with assistance.

Jonglei, the largest state in the eastern part of South Sudan, has been the scene of inter-communal violence since the African country won its independence in July 2011. Nuer and Murley, the biggest tribes in the state, have been locked in clashes due to disputes over land and cattle ownership.

The South Sudanese government has earlier declared Jonglei state a "disaster area" and sent around 3,000 soldiers to try to avoid tribal violence in the state. Around 1,000 UN troops are also deployed in the area.

Armed rebels on Tuesday opened fire on a United Nations convoy with peacekeepers aboard in the Jonglei state, killing five of the peacekeepers primarily made of Indian soldiers and at least seven civilians, reports said.