"The current crisis comes on top of an already challenging humanitarian situation in the country," Valerie told a press briefing following at the conclusion of a three-day visit to assess the humanitarian situation in the country.
"[Some] 3.7 million people are now severely food insecure," she said.
She asserted that the humanitarian needs in South Sudan are far more challenging and higher than what aid agencies are able to provide.
"Humanitarian agencies have been providing healthcare, food and good sanitation to many who sought refuge in the UN bases but so far these are too little compared to the multitude sheltering in other bases around the country," lamented the UN official.
"I am proud of the work of humanitarian organizations in the country who remained during this tense and difficult period and delivered urgently needed humanitarian aid."
South Sudan has been shaken by violence since mid-December, when president Salva Kiir accused his sacked vice president, Riek Machar, of standing behind a failed coup attempt against his regime.
More than 10,000 people have reportedly been killed in the ensuing violence.
Late Thursday, the warring rivals signed an agreement in Addis Ababa – following weeks of talks – calling for a cessation of hostilities and, in principle, the release of political prisoners.
"In just over six weeks, more than 702,000 people have been displaced by the conflict across the country and another 123,000 have fled into neighboring countries," said the UN official.
She reflected on her visit Tuesday to Malakal the capital of the Upper Nile State.
"I saw people in dire circumstances; short of food, living in conditions with poor sanitation, very little water," she recalled.
"Children are not in schools and health needs continue to rise. I met women who had walked for days to seek protection and assistance; children who were being separated from their parents as they fled; and people who said they had been targeted and abused because of their ethnicity or political affiliation," she lamented.
The UN Undersecretary-General for humanitarian affairs and emergency relief coordinator said the situation was made worse by the targeting of humanitarian agencies.
"So far, aid agencies have assisted over 300,000 displaced people," she noted.
"While this has saved many lives, we have not been able to provide assistance to many others due to continuing insecurity," she regretted.
"While in Malakal, I saw UN warehouses looted and assets damaged. IOM, UNICEF and World Food Program warehouses, all looted," Valerie fumed.
"There are tens of thousands of people in the town who need our help. Because of the looting we cannot help as many as we would wish," she regretted.
She also said aid workers have been a target in the crisis.
"Aid workers have been subjected to violence, with three of our colleagues killed since 15 December," confirmed the UN official.
"I have received worrying reports of interference in humanitarian activities, including a recent incident where 106 aid workers were prevented from relocating from Yirol in Lakes State to Juba for safety."
The UN official said all these elements have affected the ability to assist all people in need.
"The development gains made in South Sudan over the last two years have been severely dented by the recent conflict," Valerie regretted.
"I strongly call on all parties to respect their obligations under international humanitarian law and ensure that all civilians are protected, regardless of who they are or where they come from."