President Donald Trump moved Friday to create a blacklist of countries that Washington says unjustly detain Americans, spelling out harsh punishments including bans on travel.

In an executive order, Trump said the United States will now designate "state sponsors of wrongful detention," similar to the powerful tool of branding countries as state sponsors of terrorism.

"With this EO you are signing today, you are drawing a line in the sand that U.S. citizens will not be used as bargaining chips," Trump aide Sebastian Gorka told reporters in the Oval Office.

The Trump administration did not immediately name countries for the new blacklist. But a senior official said that China, Iran, and Afghanistan would be under review, as they "persistently participate in hostage diplomacy."

The countries designated by the State Department would be subject to sanctions and U.S. export controls, and officials involved in the imprisonment would be barred from entry.

In one measure rarely taken by the United States, officials said that the State Department could bar U.S. citizens from visiting countries put on the blacklist.

Currently, the United States strictly bans its citizens from traveling only to North Korea, a step taken after American student Otto Warmbier was detained in 2016 in the totalitarian state and released the following year in a vegetative state. He died shortly afterward.

The new blacklist can also target groups that effectively control territory but are not recognized as states.

The United States across administrations has put a top priority on freeing Americans overseas, negotiating prisoner swaps to free high-profile detainees including in Russia.

Trump has trumpeted his record on freeing Americans, with officials saying 72 prisoners have been released overseas under his watch.

A U.S. official said that the new executive order would make it easier to take action without going through a "burdensome" process.

The United States can also remove countries if it decides they have come into compliance.

The State Department routinely helps Americans detained overseas and then assesses whether they were jailed for wrongful reasons, including as political bargaining chips.

Under former President Joe Biden, China released all Americans considered wrongfully detained in part in return for the United States loosening a warning against Americans traveling to the Asian power, advice that had hurt the business climate.