Juba - South Sudan's labour minister resigned on Friday and declared allegiance to rebel leader Riek Machar, making him the second top official to quit in the war-torn country this week.Gabriel Duop Lam, who joined a unity government last year as a member of Machar's opposition, did not give a reason for his resignation in a statement released to the press, but declared his "full allegiance and commitment" to the exiled rebel.Information Minister Michael Makuei confirmed to AFP that Lam as well as his deputy had "defected" and had left to Khartoum."It will not have any impact and it is just individual behaviour. Those who have gone away have their right to go," he said.Lam's resignation comes just days after Lieutenant-General Thomas Cirillo Swaka, the country's deputy chief of general staff for logistics, quit.Swaka accused President Salva Kiir and top members of his majority Dinka tribe of "ethnic cleansing" and of blocking efforts to implement a 2015 peace deal.War broke out in oil-rich South Sudan in 2013, just two years after it achieved independence, after Kiir accused his former deputy Machar of plotting a coup.An August 2015 peace deal, which led to the formation of a unity government, was left in tatters when fighting broke out in Juba in July last year.The opposition split in two between those loyal to exiled Machar who were no longer represented in government, and those loyal to new vice-president Tabang Deng.Lam chose to remain in the government. 'Catastrophic for civilians' Violence, often along ethnic lines, has spread throughout the country with no prospects for peace in sight and the United Nations has warned of potential genocide and ethnic cleansing.A confidential UN report obtained by AFP this week cites UN Secretary-General Antonio Guterres as saying the war had reached "catastrophic proportions for civilians".After its outbreak in Juba, the war was largely restricted to the northern states of Unity, Upper Nile and Jonglei but in the past six months it has expanded into the southern Equatoria region surrounding Juba.Former Botswana president Festus Mogae, who leads an international ceasefire monitoring team, told journalists last week that new militia groups were emerging in the country.The war has left tens of thousands dead and more than three million people displaced.The humanitarian crisis has been exacerbated by a severe drought which has put thousands at risk of famine in the country. The UN's humanitarian office OCHA said some 7.5 million people in the country were now in need of humanitarian assistance.