A new surge in violence in South Sudan's civil war is having "devastating impact" on thousands of people ahead of peace talks that are now set to resume next month, the United Nations said on Friday.The UN statement reported gunfire overnight near a temporary peacekeeping base in Leer where 600 civilians have sought shelter in recent days."More than 30 humanitarian workers have been relocated over the past two weeks because it is too dangerous for them to operate in the midst of the escalating conflict. Thousands of people have fled into swamp," the UN said of the new clashes in the Unity, Jonglei and Central Equatorias regions.The regional bloc that has been mediating the peace talks in neighbouring Ethiopia says the next round will be May 17-21. The talks had been delayed by weeks amid disagreements by the warring parties.The success of the talks depends on all sides committing themselves to ending the violence, said the head of the UN mission in South Sudan, David Shearer. He said UN teams on the ground have been reporting incidents of "killing, sexual violence, homes being burnt to the ground, cattle raiding and the looting of hospitals and schools."International frustration has been rising with the lack of progress toward peace in South Sudan, where untold tens of thousands have been killed since fighting began in December 2013. A cease-fire in December was violated within hours.South Sudan's government says it is committed to peace, but President Salva Kiir this week brushed aside opposition demands that he show it by stepping down."What is my incentive in bringing this peace if it is peace that I will bring and then step aside?" Kiir asked while speaking at the funeral of a former army chief.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.