This article has been updated to include a statement from UN Secretary General Ban Ki Moon.

The Saudi-backed Yemeni government has declared the head of the United Nations' human rights office in the country "persona non grata," just days after investigators published further evidence of civilian deaths resulting from Saudi Arabia's intervention in the country.

Rupert Colville, spokesperson for the UN Office of the High Commissioner for Human Rights (OHCHR), said a minister in the Yemeni government conveyed the decision to his office. The OHCHR Representative in Yemen, George Abu al-Zulof, is currently outside the country, and may now be unable to return. Earlier, the government-linked news agency Sabanew.net quoted an official as saying the representative had "lost professionalism and is persona non grata."

"This is very regrettable," said Colville. "We believe our office in Yemen has been doing an excellent job in very difficult conditions. We are awaiting an official written confirmation of this decision, but in the meantime will study the various accusations against our Representative and his team contained in the Government's public statements, and will respond in greater detail in the near future."

On Thursday evening, Secretary General Ban Ki Moon condemned the expulsion of al-Zulof. In a statement, his spokesperson said that in light of the decision, Ban was now "extremely concerned about the safety of the remaining national and international staff," in Yemen.

"OHCHR is actively and effectively helping to document these violations and promote and protect their [Yemenis] rights," said Ban's spokesperson. "By impeding the United Nations' human rights work, the Government is failing to uphold its obligations. Doing so can only be harmful for the country's return to peace and stability."

On Tuesday, OHCHR released new figures on casualties in the conflict. In December, at least 81 civilians were killed, 62 of whom in attacks attributed to the Saudi-led coalition, which has bombed Yemen since late March with the stated goal of reinstating President Abd Rabbuh Mansur Hadi. According to the UN, more than 2,795 civilians have been killed in Yemen since the start of Riyadh's intervention. The Shiite Houthis, who are fighting the Saudi-led coalition, and their allies loyal to former President Ali Abdullah Saleh have been documented firing indiscriminately into civilian areas, killing at least hundreds. But the majority of deaths in the last nine months, as was the case in December, have been tied to coalition bombs.

Watch the VICE News documentary Inside War-Torn Yemen: Sanaa Under Attack:

In its latest findings, the UN also referenced what it called "alarming information on the alleged use of cluster bombs by coalition forces" in Hajjah Governorate. Such weapons are prohibited under an international convention; Saudi Arabia, however, is not party to the the treaty, nor are several other coalition partners, nor is the US, which provides the coalition with logistical and intelligence support and has sold its members cluster bombs. On the same day, OHCHR separately confirmed that additional airstrikes had pummeled the capital Sana'a that morning, including one that damaged a center offering rehabilitation services for the blind.

On Thursday, Human Rights Watch reported that the Saudi-led coalition was deploying cluster munitions in Sana'a. VICE teams on the ground have previously documented their use by Saudi Arabia in the northern province of Sa'ada during a 2009 intervention there.

The OHCHR's relationship with Riyadh has worsened in recent months. In September, High Commissioner Zeid Ra'ad Al Hussein called for the creation of an independent, international human rights mechanism to investigation violations in Yemen. Shortly after, the Netherlands floated a resolution at the UN's Human Rights Council that would have created such a body, but the move was ultimately defeated after intense pressure from Gulf states. Instead, an alternative Saudi-authored text was passed, which only called on OHCHR to support a national inquiry run by Hadi's government. The Saudi government has controversially funded much of the UN's relief operations in Yemen; OHCHR notably refused to take any money from Riyadh.