This photo taken from a vehicle Thursday, Oct. 30, 2014, shows silos in the oil fields of Paloch, South Sudan.

The United Nations on Friday said it was launching an investigation and demanding accountability after eight civilians were killed earlier this week by shells fired at its compound in the town of Melut, near South Sudan’s Paloch oilfields.

Initially a South Sudanese official had said four people were killed on Wednesday by two mortar bombs. But U.N. deputy peacekeeping chief Edmond Mulet said the death toll was eight and that nearly two dozen shells were fired at the U.N. peacekeeping site by combatants.

“Today it’s calm,” Mulet told reporters, though he added that it was not clear how long the lull would last given the recent dramatic escalation of bloodshed in the area.

“We have evacuated most of our non-essential civilian staff” from Melut, he said, noting that the 120 blue-helmeted U.N. troops, 15 police and other key U.N. staff would remain. “We will stay there in order to protect civilians.”

Forces loyal to President Salva Kiir and rebels allied with former Vice President Riek Machar have been fighting for nearly18 months in the world’s newest state, which seceded from Sudan in 2011. Several cease-fires have been agreed but broken.

On Tuesday, the rebel SPLA-in-Opposition told oil firms to shut down and evacuate workers from the Paloch oilfields and said its fighters had captured the area of a refinery under construction in Melut.

U.S. Ambassador Samantha Power said the Melut attack was “only the latest in a series of brutally violent acts against civilians, including the raping and murder of children.”

Mulet said the U.N. was investigating the attack to determine who fired the shells, adding that whoever was responsible needed to “stop targeting the U.N. premises.”

He said the U.N. peacekeeping mission in South Sudan, UNMISS, was mobilizing additional troops to reinforce the U.N. forces in Melut, where at least 1,600 civilians are seeking protection.

Targeting peacekeepers or humanitarian workers is considered a serious war crime.

Mulet said that was why it was necessary to hold accountable those responsible for the attack. He said U.N. officials had complained to the South Sudanese government and rebel leader Machar, demanding that the targeting of U.N. sites cease. Mulet said he had informed the U.N. Security Council as well.

The Security Council has threatened to blacklist anyone undermining security or interfering with the peace process in South Sudan, but it has not sanctioned anyone yet.

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