Republican-affiliated U.S. experts on Asia plan to issue a joint letter expressing serious concern about Donald Trump's foreign policy, one of the experts said Monday.

The letter will be the latest in a series of statements that former Republican administration officials and national security and foreign policy experts have adopted in opposition to the foreign policy views of the Republican presidential nominee.

"I signed a letter last week of senior national security officials declaring that Mr. Trump would be the most reckless president in American history," Michael Green, a former White House official in the George W. Bush administration, told Yonhap News Agency.

"This new letter is not as high level, but focuses on Asia experts from previous Republican administrations," said Green, currently Japan chair at the Center for Strategic and International Studies, a major think tank in Washington.

Green said that his reasons for opposition to Trump include "his supreme egoism and unwillingness to make any effort to study complex internal problems; his continued extreme statements that unnerve key allies and incite hatred at home; and the mounting evidence that he is unwilling to change his ways."

"Trump's statements on the US-ROK alliance in particular are dangerous and stupid," Green said. "We felt that we had little opportunity to shape his views and would do far more good by making our deep concerns public and pushing the growing momentum against his candidacy."

Green said that Republican experts are not completely endorsing Democratic presidential nominee Hillary Clinton because she has also been less than internationalist with respect to trade and government deficits. Still, however, Clinton is "otherwise quite solid," he said.

Concern has been widespread about the potential negative effects Trump could have on alliances if he is elected. The real-estate tycoon has expressed deeply negative views of alliances and U.S. security commitments overseas, seeing them as a cumbersome burden sucking up taxpayer dollars.

Trump has long argued that the U.S. should no longer be the "policeman of the world," claiming it makes no sense for the U.S. to pay to defend such wealthy allies as Japan, South Korea and Saudi Arabia in exchange for little.

He says 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. (Yonhap)