Chairperson of the African Union Moussa Faki says restrictions must be imposed on those who are disturbing peace in South Sudan following a nearly four-year civil war in the African country.

"The time has come to sanction those who are blocking peace," Faki said in an address to the opening of the 30th annual African Union summit in the Ethiopian capital, Addis Ababa, on Sunday.

He deplored the "unbelievable cruelty" and "senseless violence" of warring sides in South Sudan.

Civil war broke out in South Sudan in December 2013 just two years after gaining independence, when disagreements between President Kiir and then Vice President Riek Machar turned into an armed conflict between their loyalists. While fighting generally subsided early last year, clashes once again intensified in July 2016.

Tens of thousands of people have died and more than four million people have been driven from their homes, while millions of others are suffering from hunger in a humanitarian crisis expected to worsen as the lean season sets in.

The UN and international rights groups have on numerous occasions accused both Machar’s loyalists and government troops of committing atrocities during their military operations.

A team of United Nations rights experts in December deplored the atrocities committed by all conflicting sides in South Sudan, urging punishment of the perpetrators.

"We are deeply disturbed by what we witnessed and heard throughout our visit. The deprivation and range of sexual violence are hard to describe, people are targeted and suffering just for being who they are," Andrew Clapham, one of the UN experts, said in a statement.

The United Nations Children's Fund (UNICEF) earlier this month warned that South Sudan risks losing a generation with 70 percent of the country's children out of school due to the civil war.

"70 percent of the children are out of school, that is highest in the world. There is too much violence," Henrietta H. Fore, UNICEF's executive director, said after visiting some of the areas most devastated by the war.

South Sudan’s government and rebel groups inked a ceasefire agreement in December after talks in Addis Ababa. The deal, described by the UN as a "last chance" to stop the civil war, lasted just hours before warring parties accused each other of breaking it.

The United States once again called for an arms embargo last week in front of the UN Security Council as previous efforts in this regard have failed with some member states arguing that the move would be counterproductive to peace efforts.

US Ambassador to the UN Nikki Haley told the Security Council on January 5 that the South Sudan government was "increasingly proving itself to be an unfit partner" in efforts to restore peace.

A South Sudanese Foreign Ministry official on Friday reacted angrily to Haley's remarks, saying they would undermine relations between the US and South Sudan.