It is not fresh news that US President Donald Trump puts priority on “America First” -- a mere euphemism for the pursuit of the selfish interests of his country -- at the expense of others, including allies and friends. But his latest comments on the costs for keeping US forces overseas should raise new concerns, especially in connection with the stalled endeavors to denuclearize North Korea.

In a Twitter post earlier this week, Trump said the US is “substantially subsidizing the militaries of many very rich countries all over the world, while at the same time these countries take total advantage of the United States, and our taxpayers.”

It was not first time the US leader accused its allies -- such as South Korea, Japan, Germany and Saudi Arabia -- of being “free riders” under the US security umbrella. But his latest comments drew attention because they came shortly following the breakdown of negotiations between Seoul and Washington over the sharing of upkeep costs for American troops stationed in South Korea.

The two allies have held rounds of talks this year, but failed to reach an agreement on how much the South Korean side should shoulder over the next five years.

South Korea contributed about 960 billion won ($854 million) this year to finance the 28,500 American troops here. Reports said the US side wanted Seoul to raise its share by 50 percent to 100 percent. After the last round of talks in Seoul last week, South Korean officials said the two sides narrowed their differences, but the fact that they failed to set a date for the next meeting indicated an agreement was hard to come by.

Trump’s tweets gave strong indication he intervened in the negotiations. He said outgoing Defense Secretary James Mattis did not see the military cost-sharing issue as a problem. “I do and, and it is being fixed,” he said.

The comments confirmed that Mattis had differences with Trump not only about the president’s decision to pull US troops from Syria but also about allies’ sharing of upkeep costs for overseas US troops. It is certain that Mattis’ exit will affect the upcoming negotiations between South Korea and the US.

More worrisome is that Trump may seek to withdraw or reduce American troops from this region in the absence of a complete denuclearization of North Korea.

Trump has already mentioned his hope to pull out US troops from South Korea eventually, mostly for the sake of saving US taxpayers money. He also disclosed his obsession with money when he tied the decision to halt joint military exercises with South Korea to saving military spending.

With the denuclearization process stalled for months, the worst-case scenario could be Trump agreeing to a half-baked denuclearization of North Korea, and using that as a pretext to reduce the US military presence on the Korean Peninsula -- or other means of saving US military expenses.

These are among the reasons the recent US conciliatory gesture toward North Korea cannot be received only with open arms. In another Twitter post, Trump said progress was being made in negotiations with North Korea and that he looked forward to a second summit with Kim.

Trump posted the tweet, along with a photo he called “Christmas Eve briefing,” after Stephen Biegun, the US special representative for North Korea, visited South Korea, where he announced plans to lift a ban on US citizens traveling to North Korea for humanitarian work. During Biegun’s visit to Seoul, the US also agreed to exempt from sanctions against the North the South Korean-led project to link the two Koreas’ railways and roads and the plan to provide Tamiflu flu medication to the North.

If such an olive branch is purely aimed to draw the North back to denuclearization talks, that would be fine. But what we should guard against is Trump appeasing the North in a mediocre disarmament agreement. He may seek to tout a major foreign policy feat and exploit it as fulfilling his “America First” obsession.