MILWAUKEE (REUTERS, AFP) - The United States Coast Guard said on Thursday (June 15) 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 South-east 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 AP 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.

The actions were taken out of an abundance of caution after a "conspiracy theorist" made a claim about a threat aboard the Memphis on YouTube, Coast Guard Sector Charleston spokesman Lt. James Zorn told local WCIV television earlier.

A man named George Webb claimed the Memphis was carrying a "dirty bomb" after it had been loaded in Pakistan during a recent trip, he said. However, there was no credible information the threat was real, Zorn added.

The threat came at around 8 pm local time (7am Singapore Thursday), the Coast Guard said.

The Maersk Memphis, a 300m vessel, was in New York before arriving in South Carolina at about 7.30pm, according to Reuters data.