Mass killings in South Sudan

South Sudan's President Salva Kiir is committed to begin talks with rebel leader Riek Machar, the country's former vice president, to end fighting, a senior US official said after meeting Kiir in Juba.

"President Kiir committed to me that he was ready to begin talks with Riek Machar to end the crisis without preconditions as soon as his counterpart is willing," said US special envoy to South Sudan, Donald Booth on Monday.

It was not immediately clear how soon a meeting could be arranged.

Reports say that more than 200 people, mostly from the Nuer ethnic group, were shot by security forces.

Another man in Juba said gunmen from the majority Dinka ethnic group were shooting people in Nuer areas.

The violence comes amid a power struggle between President Salva Kiir, a Dinka, and his Nuer ex-deputy.

South Sudan's government has denied it is behind any ethnic violence.

The reports emerged as UN Secretary General Ban Ki-moon called on the Security Council to add 5,500 UN troops to the 7,000-strong force in South Sudan.

Rebels supporting sacked former vice-president Riek Machar have seized major towns over the past week.

Tens of thousands of people have fled the fighting.

The violence began last week when Kiir, a member of the majority Dinka ethnic group, accused Machar, a member of the rival Nuer ethnic group, of attempting to seize power by force.

Kiir also detained 11 politicians, some of them former ministers, in connection with the "foiled coup".

Booth said he visited the detained officials who were "secure and well taken care of."

"These individuals communicated to me their desire and their readiness to play a constructive role in ending the crisis through peaceful political dialogue and national reconciliation," he said.

President Kiir said on Monday that the army will step up the fight against rebels with imminent strikes in Bor and Bentiu, but it is not clear whether this will still take place.

Meanwhile, the US military deployed about 150 marines to a base in the Horn of Africa to prepare for possible further evacuations of US citizens from the deepening conflict in South Sudan, US officials said on Monday.

The deployment of a special crisis-response team of marines, who are normally stationed at Moron Air Base in Spain, follows a thwarted evacuation attempt in South Sudan over the weekend in which four US soldiers were wounded by gunfire.

Three US officials, speaking to Reuters on condition of anonymity, said the Marines were sent to a base in Djibouti, a move that would allow them to deploy to South Sudan more quickly, if asked.

Meanwhile, United Nations (UN) chief Ban Ki-moon asked the UN Security Council on Monday to send 5,500 more peacekeepers in South Sudan to better protect civilians from violence that threatens to plunge Africa's youngest country into civil war. 

There are currently some 6,700 UN troops and 670 police officers in the UN force in South Sudan, which is known as UNMISS.

US envoy to the UN, Samantha Power, said, "the [US] is eager to work to make sure the mission has the assets to fulfill its mandate." 

French ambassador to the UN Gerard Araud told a press conference that a decision about the proposal will be made at 3pm local time on Tuesday.