NEW YORK -- US President Donald Trump said Monday on social media that 25-percent tariffs will be imposed on imports from Japan and the Republic of Korea, respectively, beginning Aug 1.

In his letters addressed to the leaders of the two countries, Trump said the new tariffs will be separate from all other sectoral tariffs.

Later on, he announced that similar letters were sent to the leaders of 12 other countries, namely Malaysia, Kazakhstan, South Africa, Myanmar, Laos, Tunisia, Indonesia, Bangladesh, Serbia, Bosnia and Herzegovina (BiH), Cambodia, and Thailand, informing them that tariffs ranging 25 percent to 40 percent will be charged starting next month.

The tariffs rate on Malaysia, Kazakhstan and Tunisia will be 25 percent, and it will be 30 percent for South Africa and BiH. Indonesia will face a tariffs rate of 32 percent, and Bangladesh and Serbia will see 35 percent. Tariffs rate on Cambodia and Thailand will be 36 percent, and for Laos and Myanmar it will be as high as 40 percent.

In the almost identical letters, Trump asked leaders of these countries to understand that the tariffs rates number"is far less than what is needed to eliminate the Trade Deficit disparity we have with your Country."

Trump warned that if these countries raise their tariffs in response, the United States will increase its tariffs by the same amount.

He said that there will be no tariff if these countries or their companies decide to build or manufacture products within the United States, and that"in fact, we will do everything possible to get approvals quickly, professionally, and routinely -- In other words, in a matter of weeks."

He also said that "if you wish to open your heretofore closed Trading Markets to the United States, and eliminate your Tariff, and Non Tariff, Policies and Trade Barriers, we will, perhaps, consider an adjustment to this letter."

White House Press Secretary Karoline Leavitt said Monday afternoon that Trump plans to issue an executive order to extend the pause on "reciprocal tariffs" from July 9 to Aug 1.

"So, the reciprocal tariff rate or these new rates that will be provided in this correspondence to these foreign leaders will be going out the door within the next month or deals will be made," said Leavitt.

On Wednesday, Trump said that the United States had struck a trade deal with Vietnam that includes a 20-percent tariff on the Southeast Asian country's exports to the United States.