The UN Security Council on Friday expressed its outrage over recent armed attacks on civilians taking shelter at a UN base in a war-torn town in South Sudan, and called on the South Sudanese government "to bring the perpetrators of these egregious acts to justice."

"The members of the Security Council expressed their outrage at the recent attacks by armed groups in South Sudan that have purposefully targeted civilians as well as UN Mission in South Sudan (UNMISS) sites and personnel, in particular the 17 April attack against the UNMISS compound in Bor that resulted in scores of dead and injured, including those seeking the shelter and protection of the United Nations, and the 14 April attacks in Bentiu and Unity State," said a statement issued to the press here by the 15-nation council.

The Council condemned in the strongest terms these acts and underscored that attacks on civilians and UN peacekeepers may constitute a war crime.

The armed groups on Thursday used rocket-propelled grenades to attack the UN base, where 5,000 people are sheltered, killing at least 20 people and injuring 70 others, reports said.

The Security Council called on the government of South Sudan to immediately take steps to ensure the safety of all civilians and UNMISS Protection of Civilian sites in South Sudan, to swiftly investigate these incidents, and to bring the perpetrators of these egregious acts to justice, said the statement.

The Council also extended their condolences to the families of those civilians injured and killed in these attacks, calling on both parties to allow UNMISS to fully implement its mandate.

"The members of the Security Council underscored their full support for UNMISS peacekeepers and commended the actions of the UNMISS contingents in Bor as they sought to fulfill their mandate to protect civilians," said the statement. They also called on all parties to refrain from actions or statements that could further escalate the situation.

The violence that has swept South Sudan since mid-December 2013 has left thousands dead and forced around a million people to flee their homes after fighting broke out in the capital Juba between soldiers loyal to President Salva Kiir and forces who sided with former vice-president Riek Machar.

UNMISS has opened the gates at eight of its bases in the country to those seeking refuge from attacks that have taken on increasingly ethnic dimensions as the fighting has continued. Four months into the conflict, UNMISS is hosting some 67,000 civilians at its bases.