Republican presidential nominee Donald Trump said he would be "absolutely" prepared to tell U.S. allies, "Congratulations, you will be defending yourself," unless they agree to shoulder more of the cost for American troop presence.

Trump made the remark in an interview with the New York Times held a day after he officially clinched the Republican presidential nomination, once again signalling he's ready to abandon U.S. security commitments overseas unless they make economic sense.

"I would prefer that we be able to continue (protecting other countries), but if we are not going to be reasonably reimbursed for the tremendous cost of protecting these massive nations with tremendous wealth ... I would be absolutely prepared to tell those countries, 'Congratulations, you will be defending yourself,'" Trump said, according to the interview transcript.

Making allies pay up for an American troop presence has been one of the top foreign policy priorities for Trump. The real-estate businessman hasn't backed down, arguing that it makes no sense for the U.S. to help defend such wealthy allies as Japan, South Korea and Saudi Arabia in exchange for little. He also says the U.S. can no longer afford to be the policeman of the world.

He has often said that allies should pay 100 percent of the cost of stationing American troops, or the U.S. should be prepared to end their protection. He even suggested allowing South Korea and Japan to develop their own nuclear weapons for self-defense so as to reduce U.S. security burdens.

Despite the U.S. troop presence in South Korea, Trump said, "There's no guarantee that we'll have peace in Korea."

Trump also said that even though the U.S. has kept troops in Korea since 1953, "that doesn't mean that there wouldn't be something going on right now. Maybe you would have had a unified Korea. Who knows what would have happened."

Despite the troop presence, North Korea has become stronger, he said.

"We've let North Korea get stronger and stronger and more nuclear and more nuclear," he said. "North Korea now is almost like a boiler. You say we've had peace, but that part of Korea, North Korea, is getting more and more crazy. And more and more nuclear.

And they are testing missiles all the time ... And we've got our soldiers sitting there watching missiles go up."

Trump said that compared with decades ago, the U.S. is not the same country and the world is not the same world.

"We don't have the luxury of doing what we used to do; we don't have the luxury, and it is a luxury. We need other people to reimburse us much more substantially than they are giving right now," he said.

He also criticized his Democratic rival Hillary Clinton for saying the U.S. would never abandon allies.

"You always have to be prepared to walk. It doesn't mean I want to walk. And I would prefer not to walk. You have to be prepared and our country cannot afford to do what we're doing," he said. (Yonhap)