The United Nations on Saturday called for a halt to fighting in South Sudan after the government launched a new offensive earlier this week.
South Sudanese government forces targeted a town in the north on Wednesday, displacing civilians the UN said may be headed toward the border with Sudan.
"We are disturbed by the escalation of violence and subsequent suffering of civilians in South Sudan as a result of the recent government offensive," Stephane Dujarric, spokesman for Secretary-General Antonio Guterres, said in a statement.
"We urge the government and other warring parties to cease hostilities, uphold their responsibility to protect civilians and cooperate with the United Nations and other humanitarian actors to ensure safe access to all civilians in imminent danger along the West Bank of the River Nile."
Some 50,000 people in Kodok in Upper Nile state, many of whom fled fighting six weeks ago in the town of Wau Shilluk, were at risk from the violence, the UN said earlier this week.
"The renewed upsurge in fighting represents a callous and blatant disregard of the pledges made during the 25 March 2017 IGAD (Intergovernmental Authority on Development) Summit to implement a ceasefire and to facilitate humanitarian access," Dujarric said, calling on all sides to return to the negotiating table.
"There can be no military solution to the crisis in South Sudan."
This week's attack was the latest in an upsurge in fighting in South Sudan since the beginning of the year that has driven tens of thousands of civilians from their homes.
After gaining independence from Sudan in 2011, the country descended into war in December 2013, leaving tens of thousands dead and more than 3.5 million people displaced.
In February, South Sudan and the United Nations formally declared a famine in parts of northern Unity State affecting 100,000 people, a disaster UN officials said was "man-made" and could have been averted.