South Korea has agreed to pay substantially more money to the United States in order to defend itself from North Korea.
A South Korean foreign ministry official said negotiations have not officially started. It declined to comment further on Trump's tweets.
The president noted that Seoul has paid $990 million for its share of the defense costs of keeping the more than 28,000 American troops stationed in South Korea.
"South Korea and I have made a deal where they're paying a lot more money, and they're going to pay a lot more money".
That was an increase of 8.2% from the previous annual contribution but far short of USA demands, which some reports placed as high as $1 billion.
That's likely to be a tough sell, since South Korea had already agreed to an increase past year and then had to start negotiations all over when Trump got involved and started demanding dramatically more.
Its four rounds of weapons demonstrations in two weeks come during a stalemate in nuclear negotiations and after President Donald Trump repeatedly dismissed the significance of the tests, even though the weapons show North Korea's ability to strike at USA allies South Korea and Japan and its military bases there. "The relationship between the two countries is a very good one!" Normally the agreement has been for five years.
Regarding the defense cost-sharing talks, a foreign ministry official in Seoul said the two countries have exchanged only "broad-brush views" on the issue without discussing details.
These rotations and visits are customary during periods of tension with North Korea, but also take place during joint exercises.
Trump has long complained that the United States suffers too much of a financial burden from its military deployment overseas and has specifically singled out South Korea as a nation that should spend more money for thousands of troops deployed there.
Japan has approved export of a high-tech material to South Korea for the first time since imposing tighter curbs last month, but doubled down on political pressure and warned it could broaden restrictions on shipments to its Asian neighbour.
Japan has approved the export to South Korea of some key products for the first time since introducing stricter trading rules amid an ongoing row between the two U.S. allies.