New York - South Sudan's government has shown little interest in a new regional peace initiative that the United States has described as a final chance to end the war, the UN peacekeeping chief said on Tuesday.The UN Security Council has thrown its weight behind the drive by the regional IGAD group to kick-start the peace process through its "revitalisation forum" of a 2015 deal that has failed to take hold."With regard to the revitalisation forum announced by IGAD, the government has only given a lukewarm response," Jean-Pierre Lacroix, the UN under-secretary-general for peacekeeping, told the Security Council.Led by Ethiopia, foreign ministers of the seven-nation Intergovernmental Authority on Development (IGAD) met with President Salva Kiir this month and exiled rebel leader Riek Machar in South Africa.Kiir "reportedly committed to support the forum while asking a series of clarifications on its objectives that IGAD agreed to address in writing," said Lacroix.Machar and other opposition leaders have "declared cautious support to the process," he added.US Ambassador Nikki Haley is expected to travel to South Sudan this month to press for progress in ending the war that has killed thousands and driven nearly four million people from their homes. Haley, who will be the highest-ranking administration official to visit Africa, last month said the regional initiative is "the last chance at salvaging the peace agreement."The United States is South Sudan's biggest aid provider and a key supporter of its 2011 independence from Sudan.South Sudan descended into war in December 2013 when Kiir accused Machar, his former deputy, of plotting a coup.Lacroix said recent fighting in northern Jonglei and Upper Nile as well as in the Equatoria states were "cause for grave concern."The peacekeeping chief said the coming start of the dry season could lead to more fighting.The United Nations has 17 000 peacekeepers in South Sudan, tasked with protecting civilians. More than 200 000 people are sheltering at UN bases.