The United States may apply “appropriate pressure” on government officials and rebel leaders to end the conflict in South Sudan, the State Department's top Africa official has warned.

Assistant Secretary of State Linda Thomas-Greenfield did not specify what actions the US might take, but indicated “individuals on both sides who interfere with the peace and reconciliation process in South Sudan or are responsible for serious human rights abuses” as the target.

The implied sanctions amplify the Obama administration's response to the conflict.

She reiterated the US stance that "political detainees currently being held in Juba must be released” and allies of rebel leader Riek Machar be allowed to join the talks in Ethiopia.

READ: US urges Kiir to release political detainees

A US House of Representatives panel was also told that those engaged in the violence are "breaking promises to their own people.”

The official reiterated support for the mediation process initiated by the Intergovernmental Authority on Development, saying it “offers the best hope for South Sudan and the region.”

She cited an estimate by the International Crisis Group that over 10,000 South Sudanese may have lost their lives.

“Political rivalries have taken on ethnic dimensions, atrocities are being committed, and men, women, and children are caught in the crossfire,” the senior Africa official said.

According to her, efforts to oust President Salva Kiir by force are opposed and the US is urging the South Sudanese government to open political space to allow for greater inclusion.