US Secretary of State John Kerry phoned the South Sudan President on Friday to discuss the political and humanitarian situation in the country.

Kerry heads the department of the United States Government responsible for diplomacy and for advising the president on foreign policy issues including development and military assistance.

The top US diplomat has met several times with President Salva Kiir, most recently during the referendum in January 2011, when Kerry was still chairman of the Senate Committee on Foreign Relations.

After his phone call with Kiir, Kerry announced from Washington that “lifesaving humanitarian assistance must be allowed to reach the estimated 100,000 civilians affected by the fighting” in Jonglei State.

Aid access in the state, and in Pibor County in particular, has been complicated by security factors including clashes with the David Yau Yau forces and inter-tribal fighting between the Murle and Lou Nuer.

“Those responsible for human rights violations and attacks on civilians – including members of the Sudan People’s Liberation Army – must be held accountable,” Kerry stated.

Kerry’s phone call came one week after USAID Administrator Dr. Rajiv Shah announced he was “gravely concerned” by the “escalation of the humanitarian crisis in Pibor County.”

Dr. Shah had called for the immediate relocation of SPLA garrisons out of town centers and for the removal of commanding officers with “records of civilian endangerment.”

“The people of Jonglei must be able to return to key population centers to receive urgent life-saving assistance,” the USAID director stated.

The US National Security Council met about the Jonglei situation on Wednesday, according to an announcement made on the White House website.

Grant Harris, a special assistant to President Barack Obama and a participant at the meeting, disclosed that “a significant portion of the conversation focused on what the United States and its partners can do to address disturbing reports of human rights abuses, attacks on civilians, and ethnically motivated violence taking place in Jonglei, including reports that elements of the Sudan People’s Liberation Army have been complicit in the abuses.”

Harris added that over 100,000 civilians, predominantly from the Murle ethnic group, have been displaced since May with little access to humanitarian aid.

Doctors Without Borders, or MSF, has attempted to scale up emergency aid in Pibor County together with ICRC and other organizations. But earlier this month the medical group announced that people “are afraid to seek medical care in towns,” adding that people were hiding in “malaria-infested swamps.”

Kerry also said that he was concerned about the political situation in Juba, and that he urged President Kiir to form a new government quickly.