Amid increasing violence in South Sudan a UN base in the key oil town of Melut was said to have been targeted when 22 shells struck and killed eight of the hundreds of civilians seeking shelter there.

The UN officials said targeting peacemakers can be considered as a war crime, the new agency AP reported.

The assistant secretary-general for peacekeeping operations, Edmond Mulet, told reporters that the attack in Melut in Upper Nile state is part of the worst violence the UN has seen in the South Sudan conflict.

Civilians in extreme danger

The escalating fighting in South Sudan has left hundreds of thousands of civilians without any access to medical care, the medical charity Doctors Without Borders said at a press conference in Nairobi on Friday.

People are "senselessly suffering through an entirely man-made catastrophe," UN rights chief Zeid Raad al-Hussein said on Friday. His warning came as South Sudanese government forces mounted air and ground attacks after pushing back rebels from the town of Melut.

Rebels last week launched a major counter-attack, including an assault on Malakal, which is the state capital of Upper Nile and the gateway to the country's last remaining major oil fields.

Trapped by fighting

Fighting broke out in December 2013 when South Sudan's President Salva Kiir accused his former deputy Riek Machar of attempting a coup, starting a series of retaliatory killings across the country.

More than 100,000 civilians have been sheltering in several UN bases around South Sudan since early in the fighting, when troops loyal to former vice president Riek Machar clashed with those loyal to President Salva Kiir.

ra/msh (dpa, AFP, AP)