COPENHAGEN - The US Coast Guard said on Thursday a terminal at the Port of Charleston in South Carolina will reopen and a safety zone has been lifted after investigating a "potential threat" of a dirty bomb on a container ship."Unified Command determines no existing threat to the port. Terminal will reopen and safety zone has been lifted," the US Coast Guard Southeast said on Twitter.There were four containers where a threat was posed at the terminal, it said. "These have been scanned and cleared by authorities."Maersk Line, the world's biggest container shipping company and part of A.P. Moller-Maersk, said in a statement on Thursday the US Coast Guard had informed it of a threat of a "dirty bomb" aboard one of its vessels. It said all crew members were safe and ashore.