“It is our hope that in these next days, literally, we can move more rapidly to put people on the ground,” Mr. Kerry said after a meeting here with his counterparts from Uganda, Kenya and Ethiopia.
Mr. Kerry also said that the African foreign ministers were willing in principle to join the United States in imposing economic sanctions on individuals in South Sudan deemed responsible for the violence and that the effort to mediate the conflict would be intensified in the coming days.
The violence in South Sudan has killed thousands of people, displaced more than a half-million and become the most serious humanitarian crisis in the world besides Syria, United Nations relief officials say. A cease-fire negotiated here by the government of South Sudan and rebels in January has not been observed.
The United Nations peacekeepers in South Sudan number about 7,700. Known by the acronym Unmiss, for the United Nations Mission in the Republic of South Sudan, the force has faced difficulties protecting itself, let alone the civilians who have sought refuge at its compounds.
The effort to mobilize African reinforcements to augment the force has been underway since December. But it has encountered a number of obstacles, including the reluctance of African nations to allow their forces to be integrated into the United Nations peacekeeping effort.
Mr. Kerry said that agreement had been reached in his meeting here on the “terms and timing” of the deployment of African troops who would be sent to safeguard civilians and separate warring sides in South Sudan. But details still need to be worked out. It remained unclear how many additional troops would be sent, when they might arrive, what the command and control arrangements would be and what steps the United Nations Security Council might need to take before they could be deployed.
During a visit on Wednesday to South Sudan, Navi Pillay, the United Nations high commissioner for human rights, said the need for more international troops was urgent.
“In December, the Security Council agreed that the number of Unmiss peacekeepers should be increased from 7,700 to 13,200,” she said. “But the contributing countries have still not supplied some two-thirds of the extra desperately needed troops.”
Ms. Pillay, who met with Salva Kiir, the South Sudan president, and Riek Machar, the rebel leader, said that both were to blame for the increasing violence.
“The prospect of widespread hunger and malnutrition being inflicted on hundreds of thousands of their people, because of their personal failure to resolve their differences peacefully, did not appear to concern them very much,” she said.
In his news conference here, Mr. Kerry said there were “very disturbing” indications that ethnic and tribal killings could lead to full-fledged genocide if more peacekeepers were not sent and diplomatic action was not taken.
“We still hope that visits with serious discussion, with clear implications to the leadership about what is at stake, and what the repercussions may be if they do not begin to move in a different direction, that that kind of effort might be able to make a difference,” Mr. Kerry said. “No promises. Might.”
President Obama issued an executive order last month that authorized sanctions against individuals who are responsible for the conflict. The sanctions, which would include a freeze on assets and a ban on travel to the United States, have not yet been imposed. But American officials acknowledge that they are unlikely to be effective until Kenya, Uganda and Ethiopia take similar measures.
“We have not decided on a list of who the individuals are yet,” a senior State Department official said Wednesday, referring to the American sanctions that are being weighed. “A lot of the South Sudanese own property and travel to Kenya and Uganda and Ethiopia. And so without them participating, we think the sanctions will be weaker.”
Mr. Kerry said that the United States was prepared to impose sanctions unilaterally, if need be. He expressed hope that African nations would take similar actions, though what the steps might be and when they might be taken remained unclear.