Washington - The International Monetary Fund said on Wednesday South Sudan had become the institution's 188th member country, giving it access to IMF loans and technical assistance."South Sudan faces enormous challenges, and the IMF will do its best to assist the country in setting up the foundations for economic stability and growth in the period ahead," IMF managing director Christine Lagarde said.South Sudan became independent last July, under a 2005 peace agreement that ended decades of civil war with Sudan in the north. It has been struggling to tackle an economic crisis and contain tribal and rebel violence. Peace with Khartoum remains uneasy, with the north and south deadlocked over oil transit fees.The IMF said it was providing technical help and training for South Sudan government officials. It was also coordinating with donors on a trust fund to help the country. Oil makes up 98% of state revenues in South Sudan, one of the world's least developed countries.