JUBA, South Sudan — South Sudan President Salva Kiir on Wednesday signed a peace deal with rebels, more than 20 months after the start of fighting between the army and rebels led by his former deputy. Machar, the former deputy president, signed the agreement last week in Ethiopia but Kiir refused, saying he needed more time, drawing condemnation from diplomats who want a quick agreement to end the violence in the world’s newest country. Kiir was under intense pressure to sign the compromise accord mediated by a group of neighboring countries, with the U.S.