New Delhi, March 5 -- More than two dozen Doctors Without Borders workers remain unaccounted for a month after attacks in South Sudan, the medical charity said.

Two facilities operated by the group, known by French acronym MSF, were attacked on Feb. 3 in Jonglei State, northeast of the capital, Juba, where violence has displaced an estimated 280,000 people since December.

A hospital in the town of Lankien was bombed by government forces, MSF said, while another medical facility in the town of Pieri was raided by "unknown assailants." Both were located in opposition-held areas.

Staff working at the two facilities fled alongside much of the local population into deeply rural areas where armed clashes and aerial bombardments were ongoing....