UNITED NATIONS, Dec. 23 -- UN Secretary-General Ban Ki- moon on Monday said that he will ask the Security Council to reinforce the peacekeeping force in South Sudan as the conflict there deteriorates.

"I am determined to ensure that UNMISS (UN Mission in South Sudan) has the means to carry out its central task of protecting civilians," Ban told a news conference at UN Headquarters in New York just hours after combing back from a visit to the typhoon- ravaged Philippines.

"Also today, I will be sending a letter to the Security Council containing my recommendations for boosting the protection capacity of UNMISS with additional troops, police and logistical assets," he said.

Deadly clashes have escalated in South Sudan since last weekend, according to media reports, following what President Salva Kiir's government claimed was an attempted coup by soldiers loyal to former Vice President Riek Machar, who was dismissed in July.

Earlier Monday morning, Ban convened a crisis management meeting of his top advisers on the worsening situation in South Sudan, with his Special Representative for South Sudan Hilde Johnson and Special Representative to the African Union Haile Menkerios joining in by video conference.

"The situation is of mounting urgency. I am especially worried by reports of ethnically targeted killings," Ban said. "Tens of thousands of people are displaced, including some 45,000 seeking protection at the bases of our Mission, UNMISS."

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

On Saturday, UNMISS relocated all remaining civilian staff from its compound in the Jonglei state capital of Bor to Juba,

"I will be spending most of today calling regional leaders and others to bolster military support for UNMISS, as well as political backing for efforts to defuse the crisis," he said of the force, which currently has over 6,800 troops and police in the country.

"We are already approaching countries to help meet the new requirements. We are also looking at other peacekeeping missions, while taking care not to reduce their capacity to respond to threats where they operate," he added.

The UN secretary-general also commended the "brave peacekeepers " as well as the staff and leaders of UNMISS, which "is protecting civilians at its bases, supporting humanitarian deliveries, monitoring the human rights situation and investigating reports of abuses."

"Let me be absolutely clear. The world is watching all sides in South Sudan. Attacks on civilians and the UN peacekeepers deployed to protect them must cease immediately," Ban said. "The United Nations will investigate reports of grave human rights violations and crimes against humanity. Those responsible at the senior level will be held personally accountable and face the consequences -- even if they claim they had no knowledge of the attacks."

He stressed that he has repeatedly called on President Kiir and opposition leaders to come to the table and find a political way out of this crisis.

"Whatever their differences may be, they cannot justify the violence that has engulfed their young nation," he said. "They must do everything in their power to immediately ensure that their followers hear the message -- loud and clear -- that continued violence, ethnic and otherwise, is completely unacceptable."

The UN chief noted that it is time for South Sudan's leaders to show their people and the world that "they are, above all, committed to preserving the unity of the nation that was born out of their long struggle for independence."

Ban also appealed directly to the people of South Sudan, pledging full UN support.

"The United Nations stood with you on your road to independence, " he declared. "We will stay with you now ... We will do our utmost to protect you, to provide the humanitarian assistance you need, and most of all to help the country re-gain the path to peace."