Story highlights Thousands of people have been killed since clashes erupted in December

"The hard journey on a long road begins now and the work must continue," John Kerry says

UK diplomat hails the cease-fire deal

South Sudan 's President has reached a cease-fire deal with a rebel leader following five months of violence in the world's youngest nation.

The deal signed Friday in the Ethiopian capital of Addis Ababa comes a week after U.S. Secretary of State John Kerry met with President Salva Kiir.

During the meeting, he pushed for Kiir to hold face-to-face talks with rebel leader Riek Machar.

"I saw with my own eyes last week the stakes and the struggles in a new nation we helped courageous people create," Kerry said Friday after the deal.

"The people of South Sudan have suffered too much for far too long. In this most recent crisis alone, over one million people have been displaced, even more now face the prospect of famine ... there have been human rights abuses on a massive scale committed by both sides."

Thousands of people have been killed and more than 1.3 million displaced since clashes erupted in December between forces loyal to the two rivals. The parties signed an initial peace deal in January, but it fell apart days later.

Kerry welcomed the new peace agreement, saying it "could mark a breakthrough for the future" of the young nation.

"The hard journey on a long road begins now and the work must continue," he said.

Mark Simmonds, British foreign minister for Africa, hailed the "long overdue step" but noted the persistence of fighting despite the deal.

"It is essential that both sides ensure its immediate implementation and take full responsibility for the forces under their control. Only with continued engagement and the genuine commitment of both sides will South Sudan be able to pull back from catastrophe," he said.

"This conflict has caused innumerable deaths, forced hundreds of thousands of people from their homes, and brought the country to the brink of famine."

The violence started late last year after Kiir accused Machar of trying to oust him through a coup, a charge he denied.

Since the attempted coup, violence spread rapidly, with reports of their forces conducting mass killings nationwide. The violence ran down ethnic lines --- the Nuer tribe backs the rebel leader while the President hails from the Dinka tribe.

In April, militia seized the strategic oil town of Bentiu, separated terrified residents by ethnicity and slaughtered at least 400, the United Nations said.