Land access to a vital supply port in the Haitian capital of Port-au-Prince is being closed off after attacks by armed gangs, operator Caribbean Port Services (CPS) said on Thursday.'CPS will shut its barriers to all types of land-based traffic from Sept. 26 to Sept. 29,' it said in a statement, saying that the suspension should allow the army and national police to secure the area.A shipping official told Reuters this week that ships were being shot at…