The United States Coastguard says it will increase security checks on any ships which have recently docked in Solomon Islands or Nauru.
The two countries are the only ones in the Pacific Islands region which are on the first US watchlist after new shipping and port security laws were introduced worldwide.
The US Coastguard says ships docking in either country could tighten security and report to US officials before their arrival, or face costly delays.
The US Coastguard says it will increase boardings of ships bearing the Cook Islands flag, after what it calls two months of below average compliance with the international security standards.
