The U.N. chief called for an immediate arms embargo of South Sudan on Monday, amid renewed fighting between government and opposition forces in the capital.

Secretary-General Ban Ki-moon also called upon the Security Council to fortify the peacekeeping force in South Sudan and slap additional sanctions on leaders blocking implementation of the peace agreement.

"The renewed fighting is outrageous," Ban said. "It is yet another grievous setback. It deepens the country's suffering. It makes a mockery of commitments to peace."

President Salva Kiir and former rebel leader Riek Machar, now vice president, signed a peace accord last year and formed an uneasy transitional coalition government. But fighting continued despite the peace agreement and the current clashes in Juba threaten to plunge the parts of South Sudan that had been relatively stable back into violence.

Explosions and heavy weapons fire continued for a fifth day Monday, including attacks by government forces on the U.N. peacekeeping base and a camp housing some 28,000 thousand displaced civilians. An additional 3,000 civilians have sought shelter at the U.N. base to escape the immediate fighting.

There were eight deaths and 67 injuries at the U.N. base Sunday and Ban singled out the killing of two Chinese peacekeepers for condemnation. He said the compound was caught in a "crossfire."

South Sudan's president on Monday ordered the army to cease hostilities and protect civilians, effective immediately.

Ban did not elaborate on the degree to which U.N. forces in South Sudan could be bolstered, saying he would discuss it with the Security Council. The U.N. currently has 12,000 peacekeeping troops and police in South Sudan.