A fresh bid to end 17 months of civil war in South Sudan was launched by regional powers on Monday with a push to reconcile the country's president and rebel leader.

The latest peace plan, aimed at resolving a split in the country's ruling faction that ignited the carnage, comes amid mounting frustration over broken promises and failed ceasefire deals.

It involved the return to South Sudan's capital Juba Monday of a group of former political detainees, arrested by government forces as the civil war began in December 2013 and released to Kenya weeks later.

Diplomats hope the group, all of whom held influential positions in South Sudan's ruling SPLM party, will play a bigger role in ending the war between President Salva Kiir and former vice president Riek Machar.

"Today is a big day in South Sudan," South African Vice President Cyril Ramaphosa told journalists at Juba airport, where he arrived along with five former detainees.

"We have brought five of its outstanding sons back home. We brought them home as part of the process of making sure that we install peace once again in this country. This is a new face in the peace making process," he said.

The delegation also included the foreign ministers of Kenya and Ethiopia, and the head of Tanzania's ruling party, Abderhamn Kinane -- the countries which have been behind a string of unsuccessful peace initiatives.

Talks hosted by regional bloc IGAD have resulted in several deals but not peace, while parallel talks in Arusha, Tanzania on reuniting the SPLM have done little more than confuse the issues.

In the meantime, both Kiir and Machar's forces have continued to seek battlefield victories.

The civil war in the world's youngest nation began in December 2013, when Kiir accused his sacked deputy Machar of attempting a coup, setting off a cycle of retaliatory killings across the country.

The country has also been carved up along ethnic lines -- pitting Kiir's Dinka tribe against Machar's Nuer tribe -- with the focus of the fighting on the country's northern oil fields.

The latest round of fighting has cut off over 650,000 people from aid, with fighters torching towns, raping residents and looting relief supplies, according to the United Nations and aid agencies.

The United States said last month it was was working with the UN Security Council to gather evidence for possible sanctions against leaders of the warring factions.

The African Union has also demanded sanctions and an arms embargo.

Over half of the country's 12 million people are in need of aid, with 2.5 million people facing severe food insecurity, according to the UN.