The UN Security Council expressed "serious concern" on Tuesday over delays in the return of South Sudan's rebel leader Riek Machar to the capital Juba as part of a peace deal. The 15-member council met behind closed doors at the request of the United States to hear a report on the latest hurdle in the way of the agreement to end the two-year civil war. Council members "urged all parties to quickly form the transitional government and fully implement the peace agreement," said Chinese Deputy Ambassador Wu Haitao, whose country holds the council presidency.