Reports of widespread sexual violence against women and young girls in South Sudan by uniformed soldiers and other groups of armed men are "deeply disturbing" and may be regarded as war crimes as well as crimes against humanity, the UN Mission in South Sudan has warned.

In a statement released on Monday, UNMISS, which is currently providing protection to about 200,000 civilians in various locations around the country, said its advisors have documented more than 100 cases of sexual violence and rape - including gang rapes and the abuse of minors - since conflict broke out again in the world's newest nation in early July.

"The United Nations condemns unequivocally these actions, and reminds all combatants and parties to the conflict, their commanders, and responsible leaders, that these acts constitute grave violations of international human rights law and may be regarded as war crimes as well as crimes against humanity," UNMISS said in the statement.

UNMISS said it was also looking into allegations that its own peacekeeping personnel had not done enough to protect women and minors who were the victims of sexual violence and added that it has "reinforced the message to all peacekeepers that if these incidents of abuse should be committed in areas for which they have security responsibility, then they have an individual and joint duty to act, to prevent harm to innocent civilians."

It said it also continued to call on all parties to the conflict "to take personal responsibility for the immediate sanctioning of their men, in and out of uniform, who were and are responsible for these abuses and unspeakable acts of violence against civilians".

Fighting broke out in the South Sudanese capital of Juba on 8th July between forces loyal to President Salva Kiir and (now former) Vice-President Riek Machar, resulting in thousands fleeing the city. At least 300 people have been reportedly killing in the fighting since, during which UNMISS compounds and civilian protection sites have been attacked.

Despite hopes a recently agreed peace deal would bring an end to the fighting, the conflict has continued, leading humanitarian agencies to warn of a dramatically worsening humanitarian crisis in the nation.

The UN Security Council voted on Friday to extend the UNMISS mandate in South Sudan until 12th August, to allow time for discussions before a longer-term mandate can be agreed.