Editor's Note: (Princeton Lyman is the former US Special Envoy to Sudan and South Sudan (2011 -- 2013) and now serves as a senior advisor to the president of the US Institute of Peace. Nancy Lindborg is the president of the US Institute of Peace. The opinions in this article belong to the authors.)
(CNN) The situation in Syria, where civilians are being bombed each day and millions are fleeing for their lives, leaves one in despair. Years into the disaster, the politics have become so complex that it is hard to see a way to stem the bloodshed.
But there is another genocide that is looming and can be prevented: It's in South Sudan.
Reports from the UN's Special Advisor on the Prevention of Genocide, from the UN Commission on Human Rights in South Sudan, from the UN Panel of Experts on South Sudan and from every other reliable source all point to the unmistakable warning signs of an impending genocide.
Militias are mobilizing along ethnic lines, hate speech is circulating on social media, and perhaps most ominous of all, the South Sudan government's actions are already leveling villages, resulting in many dead in Central Equatoria state.
This is all happening in the context of a civil war that began in December 2013, with a steady descent since into a tribal contest between Dinka, Nuer and other ethnic groups. There have been ethnic-based killings on all sides and growing demands for vengeance.
Unlike in Syria, there are no big power contests being played out in South Sudan, the world's newest country.
Its neighboring states have been leading the search for South Sudan peace through their regional organization, the Intergovernmental Association for Development (IGAD).
Unfortunately, these countries -- Uganda, Ethiopia, Sudan, Kenya, Djibouti, and Eritrea -- all have differing and sometimes competing interests in South Sudan.
The result is a peace process that lacks firm pressure on the government of South Sudan and an unwillingness by IGAD member states yet to support either strong sanctions or an arms embargo on those threatening genocidal violence.
Yet, no solutions are possible without the support of these neighboring states.
Time is running out. All sides are actively recruiting new soldiers, including children, and stockpiling weapons.
But the worst can be prevented. IGAD members must recognize the full impact of any genocide: the horrific human costs and the much greater outflow of refugees than to date, to say nothing of the international condemnation, and the seeming failures of African Union and IGAD peace making.
IGAD leaders must make clear to the government of South Sudan, and the other South Sudan key players with whom they have contact and influence, that a major offensive as threatened by the government in Central Equatoria is unacceptable. They must also warn that sanctions will be imposed by IGAD and the international community against any party undertaking such action, and that IGAD will demand greater progress on implementing the peace plan which the various parties have signed.
In addition, IGAD must empower the African Union's Special Envoy for South Sudan, former Malian president Alpha Konare, to pursue an urgent process of mediation and negotiation to lower tensions and assure all sides of an inclusive peace process.
This task can no longer be entrusted to the government of South Sudan as proposed in the current peace plan, because the government is complicit in much of the current violence and threats of ethnic killing.
Once these measures have been taken, the 4,000 additional UN peacekeeping troops approved by the UN Security Council can be deployed with the goal of defusing ongoing tensions and providing for citizen protection, and in support of a strengthened framework for peace.
The world has spent several decades rehashing the failures that led to the Rwandan genocide.
In South Sudan there is ample warning, but the action necessary to forestall another tragedy in the region must be led by African leaders, with muscular diplomacy and clear commitment from the US, UN and world leaders.
Unfortunately, the specter of genocide is occurring at a time when the US, the UN and the African Union are all undergoing major transition.
The US administration has become deeply concerned with the situation.
The US has proposed to the UN Security Council an arms embargo on the country and economic sanctions on several key leaders on the government and opposition sides.
But passage remains uncertain as not all the African representatives are on board. Russia, China, Japan and some other members are also not supportive.
In any case, resolutions by the UN Security Council cannot substitute for high-level work with the IGAD members and the leadership of the African Union to agree on a pathway forward.
President Obama and UN Secretary General Ban Ki-moon must take this on in the waning days of their administrations.
Each should call the heads of state of the IGAD members, emphasizing the enormity and urgency of the situation and the need for stronger action.
President Obama should also dispatch Vice President Joe Biden to the region to work with those leaders on the best way forward.
Unless the current leaders of the US and UN take such initiative, they risk leaving office with the unfolding of yet one more genocide that could have been prevented.