Juba - South Sudan, independent since 2011, has been wracked for 20 months by a conflict between troops loyal to President Salva Kiir and those of ex-vice president Riek Machar.

Tens of thousands have been killed in the ethnically-motivated unrest, and more than two million people have been displaced, the United Nations figures show.

Here is a chronology of the fighting:

- 2013 -

December 15: Heavy gunfire in Juba where tensions have risen since July when Machar was fired as vice-president. Kiir denounces a coup, blaming Machar, who later accuses the president of purging his rivals. The fighting spreads to several states.

- 2014 -

January 10-20: Government troops recapture the northern city of Bentiu, capital of oil-rich Unity State, and Bor, capital of the eastern state of Jonglei. Uganda sends troops to reinforce the South Sudanese army.

February 27: Human Rights Watch says war crimes have been committed by both sides.

April 15-17: More than 350 civilians massacred in Bentiu and Bor, according to the UN's mission UNMISS.

May 2: Visiting Juba, US Secretary of State John Kerry warns of the risk of "genocide".

May 27: A Security Council decision refocuses the UN Mission on civil protection tasks.

- 2015 -

February 1: Kiir and Machar sign a new agreement to end the fighting. They have signed - then broken - at least six previous ceasefire deals since fighting began. The accord is broken several days later.

March 20: The army and rebels have kidnapped 12 000 children to fight since the start of the conflict, the UN children's agency says.

March 24: South Sudan's parliament votes to extend Kiir's mandate by three years, ditching plans for elections this year.

June 30: South Sudan's army raped then torched girls alive inside their homes, a UN rights report says, warning of "widespread human rights abuses". Rebels have also been accused of atrocities, including rape and killings.

July 1: The UN Security Council imposes sanctions on six South Sudan generals: three of them rebels and three from government forces. A day later, the US imposes sanctions on two military commanders, one from each side.

July 6: The army says it has retaken the strategic north-eastern town of Malakal from rebels.

August 11: Several rebel commanders, including Peter Gadet, a warlord hit by UN sanctions, say they have split from Machar.

August 17: The government refuses to sign a peace deal with rebels, but says it will finalise an agreement within 15 days. Machar says he signed the deal after talks in Addis Ababa.

August 18: Washington and London push for UN sanctions to punish the government.

August 25: Kiir pledges to sign a peace deal in Juba on Wednesday.