The United States on Friday sanctioned 56 vessels, shipping companies and trade businesses linked to North Korea in what President Donald Trump called the "heaviest" sanctions ever imposed on the country.

The measures, which target North Korea's attempts to evade U.N. sanctions through deceptive shipping practices, were the latest in the administration's policy of applying "maximum pressure" on the country to compel it to engage in credible talks for denuclearization.

"We imposed today the heaviest sanctions ever imposed on a country before," Trump said in an address to the Conservative Political Action Conference.

"And frankly, hopefully, something positive can happen. We will see," Trump said, expressing hope the action will prompt North Korean leader Kim Jong Un to give up his pursuit of nuclear weapons and ballistic missiles.

The measures involve 28 vessels and 27 shipping and trading companies located, registered or flagged in North Korea, China and seven other economies in Asia, Africa and Latin America, as well as one Taiwanese individual, according to the Treasury Department.

The seven other economies are Singapore, Taiwan, Hong Kong, the Marshall Islands, Tanzania, Panama and Comoros.

The United States imposed the latest sanctions on the North despite recent improvements in inter-Korean relations, suggesting the administration will step up its pressure campaign against Pyongyang in cooperation with U.S. allies and partners.

Later Friday, Trump warned that if the series of sanctions does not lead North Korea to move toward denuclearization, the United States may have to take a "very rough" step, signaling he does not rule out a military option in dealing with the country.

"If the sanctions don't work, we'll have to go phase two," he said. "And phase two may be a very rough thing. May be very, very unfortunate for the world. But hopefully the sanctions will work."

Japan informed the United States of its "strong support" for the latest action on N. Korea, Kentaro Sonoura, a special adviser to Prime Minister Shinzo Abe, said after meeting with Thomas Shannon, undersecretary of state for political affairs, on Friday in Washington.

The two allies agreed to maintain maximum pressure against Pyongyang, Sonoura said.

In Japan, Defense Minister Itsunori Onodera also backed the latest sanctions, telling reporters on Saturday in Misawa, Aomori Prefecture, "We strongly support them as they will strengthen U.S. pressure on North Korea."

Treasury Secretary Steven Mnuchin said Friday's action will "significantly hinder" North Korea's capacity to conduct evasive maritime activities that facilitate illicit coal and fuel transport, and erode its ability to ship goods through international waters.

The 28 vessels -- of which 19 are North Korean-flagged -- are "virtually all the ships" Pyongyang is currently using for its sanctions evasion schemes, Mnuchin said.

North Korea is known to falsify and conceal information displayed on North Korean vessels, and conduct ship-to-ship transfers prohibited under a U.N. Security Council resolution adopted in September.

"Through today's actions, we are putting companies and countries across the world on notice that this administration views compliance with U.S. and U.N. sanctions as a national security imperative," Mnuchin told reporters.

"The United States will leverage our economic strength to enforce President Trump's directive that any company that chooses to help North Korea fund its nuclear and ballistic missile programs will not be allowed to do business with anyone in the United States," he said.