The MV Wise Honest was stopped in Indonesia last year after it was found to be carrying coal in violation of UN sanctions.
Washington claims the 17,000 tonne ship's origin had been concealed, and it was also being used to import heavy machinery into North Korea.
The US Justice Department will investigate the ship in American Samoa's port capital of Pago Pago said the US Coast Guard's public affairs officer, Amanda Wyrick.
"The Coast Guard is working with other Federal, local and Territorial partners and we are constantly and continually doing security assessment," she said.
"We have the capabilities that if there is the need to bump up our security, we have the means to do so. We are continually assessing those [needs] and will be doing so throughout the investigation," said Ms Wyrick.