South Sudan's rebel leader Riek Machar has been sworn in as vice-president in a boost for a peace deal aimed at ending more than two years of conflict.

He returned earlier to the capital, Juba, to take the post in a new unity government led by President Salva Kiir.

Tens of thousands have been killed and about two million people left homeless in the conflict in South Sudan, which became independent in 2011.

Mr Machar fled Juba at the start of the civil war in December 2013.

He had been accused of trying to organise a coup, which he denied - but it set off a round of tit-for-tat killings, which developed into a full-blown conflict.

Both men, whose personal falling out has resulted in more than two years of bitter conflict in the world's youngest nation, spoke optimistically about the future, addressing the media at the swearing-in ceremony.

"I am very committed to implementing this agreement so that the process of national reconciliation and healing is started as soon as possible," Mr Machar told journalists at the presidential palace in Juba, AFP news agency reports.

Rare apology

Meanwhile, President Salva Kiir welcomed Mr Machar back to South Sudan, twice referring to him as his "brother", according to a transcript of his speech published by the local Radio Tamazuj news website.

"I have no doubt that his return to Juba today marks the end of the war and the return of peace and stability to South Sudan," Mr Kiir said.

The president also offered a rare apology, to the South Sudanese people and to the international community for delays in implementing the peace agreement, which was signed last August.

Earlier Mr Machar, wearing a light-coloured shirt, was greeted by ministers and diplomats as he stepped out of his plane.

Addressing the media, he said his main priorities were to ensure a permanent ceasefire, to stabilise the economy and ensure humanitarian access throughout South Sudan.

The civil war broke out over tensions between Mr Kiir and Mr Machar, who was sacked as vice-president in July 2013.

The BBC's James Copnall in Juba says once the government is formed, donors will start stumping up money - crucial as the economy is at rock bottom.

However, it is not necessarily the end of the conflict as both sides have continued to clash despite a ceasefire signed in August, he says.

There are also rebel groups which have not signed the peace deal.

South Sudan: The world's youngest country

• Split from Sudan in July 2011 after an independence referendum

• One of Africa's least developed economies. Highly oil-dependent

• Relations with Sudan strained by disputes over oil revenue sharing and borders

• Power struggle led to civil war in December 2013

• An estimated 2.2 million fled their homes during conflict

• A tentative, internationally mediated, peace agreement was signed in August 2015