The two sides of war-ravaged South Sudan will not be able to meet a May 12 deadline to form a unity government because key requirements of a peace deal have not been met, former rebel leader Riek Machar has said. Mr Machar – who would regain his post as vice president under the deal – said the government and the rebels needed another six months before forming a unity government. He spoke from Rome after attending a two-day retreat with South Sudan’s president, Salva Kiir, hosted by Pope Francis. Although few diplomats expected Messrs Kiir and Machar to meet the May 12 deadline set in last September's peace deal, the delay will cause further unease among the 12 million strong South Sudanese population. More than a third have been uprooted from their homes and around 400,000 have died in the civil war, which plunged parts of the country into famine and has been characterized by such extreme sexual violence and widespread ethnic cleansing that the UN warned in 2017 of a possible genocide. Asked if he thought the national unity government could be ready by May 12, he said: "Unfortunately, I have to say 'no'." A six-month extension was needed to unify and deploy defence forces, demilitarise the capital Juba and other cities, and agree on devolution of power and the release of political prisoners, he said. Mr Machar said he discussed the extension with Mr Kiir during a retreat at the Vatican that ended on Thursday with an appeal by the pope to the leaders to respect the armistice and resolve their differences. In a widely shared moment, Pope Francis knelt and kissed the feet of the two South Sudanese rival leaders in an unprecedented act of humbleness to encourage them to work towards implementing the peace process. "I express my heartfelt hope that hostilities will finally cease, that the armistice will be respected, that political and ethnic divisions will be surmounted and that there will be a lasting peace for the common good of all those citizens who dream of beginning to build the nation," Pope Francis said of South Sudan in his closing statement. The country’s vice president, Rebecca Nyandeng Garang, said Pope Francis' actions moved her profoundly. "I had never seen anything like that. Tears were flowing from my eyes," she said. While the leaders discussed extensions to the timeline and ways forward, the situation in Sudan – which helped broker the deal in the breakaway former province – loomed over talks. A military coup on Thursday fuelled worries that the toppling of longtime President Omar Al Bashir could derail the already fragile peace deal. "Sudan has helped us with the peace deal. We hope that the new system will also focus on the agreement, ensuring that it will be implemented," said Mr Machar, who attended an evening prayer vigil for peace, held at Rome's church of Santa Maria in Trastevere.