MANILA, Dec. 22 -- UN Secretary-General Ban Ki-moon urged all political, military and militia leaders to stop hostilities and end the violence against civilians at a press briefing in Philippines' capital region on Sunday.

"I have condemned, in the strongest possible terms, the outrageous attack in our base in Akobo on Dec. 19, where two United Nations peacekeepers were killed while protecting civilians who had taken refuge there," he said.

At least 20 civilians who sought refuge inside a UN base were killed during an attack which occurred in Akobo town, Jonglei State, on Thursday. Two Indian peacekeepers were confirmed dead, UN Mission in South Sudan said on Friday.

Ban Ki-Moon said he had called on President Salva Kiir of South Sudan and opposition political leaders, including former Vice President Riek Machar, to come to the table to find a political way out of this crisis.

They are responsible to the people of South Sudan to end the crisis and find the political means of addressing their differences, he added.

"I call on them to do everything in their power to ensure that their followers hear the message loud and clear that continued violence, ethnic and otherwise, is completely unacceptable and poses a dangerous threat to the future of their young country."

Ban made the remarks before talking about his tour to typhoon- hit areas in the Philippines as this was "a source of grave concern of the international community at this time" as he described.

The secretary-general arrived in the Philippines late Friday for a three-day visit. He toured on Saturday central Philippine city Tacloban, which bore the front of attack of super typhoon Haiyan.