As the conflict in South Sudan continues, aid agencies are struggling to provide assistance to the thousands of people caught up in the violence. As of 29 December, an estimated 180,000 people had been driven from their homes by the fighting, 75,000 of whom are seeking shelter in UN compounds."With clashes and mobilization of armed actors ongoing in several parts of the country, civilians continue to be displaced … There are reports of significant concentrations of people displaced in rural areas in Jonglei, Lakes, Warrap, and Unity states,” the UN Office for the Coordination of Humanitarian Affairs (OCHA) said in its latest update.To date some 106,000 people – around 60 percent of those in need - have been reached with some kind of assistance, according to OCHA.Aid agencies say they require an estimated US$209 million between now and March 2014 to respond to the immediate needs: $43 million has so far been received.In this briefing, IRIN looks at the humanitarian fallout of the conflict and the efforts being made to end the fighting that began in the capital, Juba, on 15 December. What are the key humanitarian needs?So far, food, shelter, water, sanitation, healthcare and protection remain the key needs of the displaced. In Jonglei State, which has experienced the brunt of the fighting, OCHA said: "In Bor, the area sheltering civilians remains congested. Sanitation is poor and the main priority is to dig additional latrines, improve provision of clean water, and continue to provide emergency healthcare.”The OCHA update added that "with poor sanitation conditions in several of the IDP sites, diseases like malaria and diarrhea affect many of the displaced people. The threat of cholera is present in several of the sites, including in UNMISS [UN Mission in South Sudan’s bases of ] Tomping and Bor.”In  a statement released on 24 December, the UN children’s agency (UNICEF) said: "UNICEF and its partners are constructing latrines, with some 400 due to be completed in coming days, and have organized and equipped teams of volunteers to clean large areas where people have had no choice but to defecate in the open for days.” The global children’s charity, Save the Children, has warned that "thousands of others, including children, are likely to have fled to the remote bush; vast swampy areas where people will likely have no shelter and will be living under trees, will be forced to drink stagnant water, and where they will have no access to humanitarian support.”Aid agencies have noted that "access to food remains limited for displaced people sheltering in UN bases around the country, and there is a need for distribution of basic food and nutrition supplies. Food needs are particularly pressing in Bor and Bentiu.”In northern Unity State, three cases of measles have been reported since the fighting broke out. According to UN sources, thousands of children below the age of 15 will receive measles and polio vaccine at the UNMISS Tomping base in Juba.Who are the most vulnerable?The conflict has left women and children highly vulnerable to abuse. An aid worker who sought anonymity told IRIN there are increasing cases of gender-based violence including rape, and some parents have lost track of their children in the congested camps."It is a bad situation and many women are exposed to violence and many are being raped. The ethnic nature of this violence and suspicion among communities has made it extremely dangerous and we have had cases where women are attacked based on their ethnicity,” she said.Save the Children has warned that thousands of children might have been separated from their parents, "with many surviving on their own in very remote and hard-to-reach areas. Save the Children is highly concerned for their safety and welfare, many of whom have witnessed their parents being killed and their homes looted or destroyed”.How has insecurity hampered humanitarian efforts?Insecurity remains the biggest challenge to humanitarian operations in South Sudan where fighting is still continuing, and increasingly marked by ethnically targeted violence between the Dinka community of President Salva Kiir and the Lou Nuer of his political rival and former vice president, Riek Machar.In Bor, the capital of Jonglei State, which has become the focus of the violence, UNICEF country representative, Iyorlumun Uhaa, told IRIN that insecurity had hamstrung efforts to reach displaced children.Relief agencies have reported that aid stocks may have been looted in the fighting that saw the town re-captured by government forces followed by a rebel counter-attack.According to OCHA, "there are serious protection concerns in all areas of South Sudan where armed violence has occurred or is ongoing. Reports continue to come in of extrajudicial killings and harassment in several locations, including credible reports of civilians being targeted and attacked based on [their] ethnic identity.”One UN worker told IRIN that limited access is affecting not only the level of assistance that can be provided, but also the level of "reliable information on the scale of the crisis”.What is being done to address the violence?The international community has engaged gears to try and end the violence in the world’s youngest nation.President Kiir has said he is ready for a ceasefire and negotiations, but Machar - who is in hiding - had previously insisted on the release of arrested allies before commiting to any truce.Regional leaders under the auspices of the Inter-governmental Authority on Development (IGAD), met in Nairobi, Kenya, on 27 December in a bid to end the hostilities. IGAD  gave the two protagonists until 31 December to commit to peace talks, and appointed a mediation team. The consequences of missing the deadline were not spelled out.But on 30 December Ugandan President Yoweri Museveni warned he would send in troops to intervene on the side of the government if the rebels ignored calls for a ceasefire.Uganda has denied claims its troops are already in the country propping up the South Sudanese military. But the conflict is potentially ripe for regional escalation, given northern neigbour Sudan's concerns over oil revenues and the longstanding rivalry with Kampala.The UN Security Council has authorized the near doubling of peacekeepers in the country – from 7,000 to 12,500. Already, the first two police units have arrived, while UN Under-Secretary-General for Peacekeeping Operations Hervé Ladsous said he hoped "all peacekeeping reinforcements will be on the ground within one to three weeks”.The UN is backing IGAD’s mediation efforts.Initial meetings in Addis Ababa between mediators and the warring parties which started on Friday have been "fruitful," according to Ethiopia's foreign minister. Tedros Adhanom told the media direct talks between the two sides, aimed at ending the violence, would begin on Saturday.