After a year and a half of civil war, millions of people in South Sudan are in danger of famine — and the situation may have just gotten even worse. The government has reportedly expelled the country's UN humanitarian coordinator, a move that signals growing tensions between the international community and the world's youngest state amid fierce fighting during the recent dry season.

The coordinator, Toby Lanzer, has overseen humanitarian operations in South Sudan since before the war began in December 2013. Lanzer has stood out among UN officials, both in South Sudan and elsewhere, with his marked public presence and constant updates on social media.

UN Secretary-General Ban Ki-moon issued a statement that condemned the move and called for the South Sudanese government "to reverse its decision immediately."

"Mr. Lanzer has been instrumental in addressing the increasing humanitarian needs of conflict-affected communities in the country, and ensuring that life-saving humanitarian assistance reaches the most vulnerable," the statement said.

The UN announced on Friday that Lanzer would soon switch positions — likely before the end of June — to become the humanitarian coordinator for Africa's Sahel region. The UN said Ghanaian Eugene Owusu, currently a UN Development Program coordinator in Ethiopia, would take over Lanzer's post in South Sudan.

The targeting of Lanzer just weeks before his expected departure appeared to reflect growing frustration by South Sudanese leaders with UN officials who have criticized the government in Juba, the country's capital. The administration of President Salva Kiir, however, still relies heavily on the UN to feed millions of its citizens, and to protect tens of thousands of people displaced by the fighting.

Ryan D'Souza, an advocacy officer at the Global Centre for the Responsibility to Protect, told VICE News that Lanzer's expulsion could be connected to the coordinator's recent condemnation of military offensives in Unity and Upper Nile stats as violations of international humanitarian law.

On May 18, Lanzer said eyewitnesses to military operations in both states had reported "targeted rape and killings of civilians, including children."

"The offensive in Unity has left thousands of homes burnt and Leer hospital is again under threat of destruction," Lanzer said.

Though Lanzer did not specifically mention the government, the Intergovernmental Authority on Development (IGAD), a regional trade bloc that includes South Sudan and seven other nations, reported days earlier that South Sudanese government forces "have been conducting full-scale military offensives against opposition forces" across Unity state. IGAD also said it was "increasingly clear the offensive" was expanding into Jonglei and Upper Nile states.

'Lanzer has criticized the government's complicity in the suffering of their own people, and for this he appears to have been punished.'

"Lanzer has criticized the government's complicity in the suffering of their own people, and for this he appears to have been punished," D'Souza said.

Fighting first broke out in Juba when rebels nominally loyal to Kiir's former vice president Riek Machar took up arms against the government. The two men hail from different communities in the country — Kiir is a Dinka, Machar a Nuer — and fighting has largely, but not always, been split along ethnic lines.

Both sides have repeatedly flouted regional efforts to broker peace, starting with a cessation of hostilities agreement in January 2014, and each has been implicated in war crimes and crimes against humanity. The International Crisis Group, a conflict monitoring organization, estimated last November that more than 50,000 people have died since the conflict broke out.

More than 130,000 South Sudanese are currently sheltering with the UN's overtaxed peacekeeping mission in the country. The mission, known as UNMISS, had its mandate renewed by the Security Council last week. At the time of its inception following South Sudanese independence in July 2011, UNMISS was largely oriented toward assisting in state building, but has since been overwhelmed caring for those affected by the conflict.

Countrywide, an estimated 1.52 million people have been displaced, and 3.8 million are classified as "severely food insecure." The UN says 874,000 children under age five currently face some sort of food insecurity, and close to one in three in the worst hit regions are malnourished. Inflation has caused the price of some food staples rise as much as 69 percent this year, putting those outside the reach of humanitarian actors at greater risk.

Lanzer's reported expulsion comes on the heels of a series of private warnings addressed to the Security Council that cite alleged misconduct by South Sudanese government officials.

VICE News obtained a letter sent to Council members on May 22 by India's UN ambassador Asoke Kumar Mukerji. The letter described the dire state of affairs at a camp for internally displaced people (IDPs) in Melut, a town in Upper Nile. Three days earlier, heavy fighting killed seven people who were sheltering in the camp and left several more wounded. Mukerji expressed alarm at the actions of government forces, saying they restricted the movements of Indian peacekeepers at the base.

"Both the troops and the IDPs have run out of water and the SPLA is not allowing the peacekeepers to fetch water from the river," Mukerji wrote, referring to the government Sudan People's Liberation Army. "There is panic among the IDPs after seeing the departure of the humanitarian component of UNMISS."

South Sudan's UN mission did not respond to a request for comment from VICE News on Monday.

In a separate confidential letter to the Council obtained by VICE News, the UN's Department of Peacekeeping (DPKO) said the situation in Upper Nile had "rapidly deteriorated" following the defection of Johnson Olony, a former government general, to the rebel side. Dated May 21, the correspondence said Olony, an ethnic Shilluk, engaged government forces in the vicinity of the camp, and that "sustained fighting with artillery, tanks, rocket-propelled grenades, heavy machines guns and small arms" resulted in the deaths of the seven IDPs.

The letter said that as of May 17, government forces had captured Guit, Koch, Leer, and Mayendit counties in Unity. The following day, Lanzer described atrocities allegedly committed in those areas.

The DPKO wrote that "UNMISS continues to receive reports of gross human rights violations, including the killing of civilians, rapes, abductions of children as young as 10 years, and the destruction of towns and villages by the SPLA and their allied forces during their military operations in Unity state."

Last week, peacekeeping chief Herve Ladsous told reporters he expected fighting to continue until the impending rainy season, which makes much of the country impassable.