UNITED NATIONS, July 10 -- The UN Security Council said Sunday that several UN peacekeepers from China and Rwanda were killed or injured in attacks in South Sudan's capital Juba, which has been hit by escalating fighting lately.

The exact number of casualties is not known yet.

The 15-nation UN body issued a statement to condemn the attacks and express condolences to the families of the peacekeepers, following an emergency session on South Sudan, a closed-door meeting that started here Sunday afternoon.

It warned that attacks against civilians and UN premises and personnel may constitute "war crimes" and assailants must be held accountable and could be subject to sanctions.

The council urged an immediate end to the fighting in South Sudan, demanding President Salva Kiir and First Vice President Riek Machar do their utmost to control their respective forces and genuinely implement their peace agreement, "including the permanent cease-fire and redeployment of military forces from Juba."

The council also encouraged regional countries, the African Union Peace and Security Council and the Inter-Governmental Authority on Development, to continue firmly engaging with South Sudanese leaders to address the crisis.

The UN Mission in South Sudan (UNMISS), acting under a 2014 Security Council resolution, has 13,490 uniformed personnel, including nearly 1,200 civilian police, plus 787 international civilians and 1,215 local civilians assigned to it.

The UNMISS' task is to protect civilians, particularly women and children against violence. This includes patrolling sites for displaced people and refugee camps and creating conditions for the delivery of humanitarian assistance.

Earlier Sunday, UN Secretary-General Ban Ki-moon said he was "shocked and appalled by the heavy fighting" in Juba, and strongly urged the leaders of the youngest country in the world to "do everything within their power" to de-escalate the hostilities.

"This senseless violence is unacceptable and has the potential of reversing the progress made so far in the peace process," Ban said in a statement issued here via his spokesman.

The fighting in Juba started on July 7 between soldiers loyal to the president and the first vice president, and has killed at least 271 people.

South Sudan gained independence on July 9, 2011 from Sudan after more than two decades of war.

In December 2013, Kiir accused his deputy Machar of plotting a coup, which was denied by the latter but led to a cycle of retaliatory killings.

In August 2015, Kiir and Machar, who was a former rebel leader, signed a peace deal which paved the way for the formation of a transitional unity government.