Security officials in Yemen say that UN envoy Martin Griffiths has arrived in the capital, Sanaa, on an unannounced visit to discuss the “complex situation” in and around the coastal city of Hodeida, AP reports. Last month, Yemen’s warring parties agreed on a ceasefire in Hodeida and on a prisoner exchange that has yet to take place. Also, under discussion from Monday will be disagreements between Yemen’s Houthi rebels, who hold Hodeida, and retired Dutch Maj. Gen. Patrick Cammaert, who is heading a UN mission charged with monitoring the ceasefire. The conflict in Yemen began with the 2014 takeover of Sanaa by the Houthi rebels. A Saudi-led coalition allied with the internationally recognized government has been fighting the Houthis since 2015.