North Korea fired two projectiles Thursday that appeared to be short-range missiles, the South’s military said, just days after it launched a presumed ballistic missile amid stalled denuclearization talks with the United States.

The projectiles were fired from the northwestern area of Kusong in an easterly direction, one of them at 4:29 p.m. and the other at 4:39 p.m., flying about 420 km and 270 km, respectively, before landing in the Sea of Japan, the Joint Chiefs of Staff said.

“Our military has strengthened surveillance and vigilance in case of a further launch from North Korea, and has maintained a full-fledged posture in close coordination with the United States,” the JCS said.

The JCS had earlier said the missiles were fired from the Sino-ri area, where the North has a base holding medium-range Nodong missiles. Kusong is about 40 km north of Sino-ri.

Any launch of a ballistic missile would violate United Nations Security Council resolutions, and South Korea’s presidential Blue House called the launches “very worrisome” and unhelpful for efforts to reduce tensions on the Korean Peninsula.

The Japanese Defense Ministry, meanwhile, said that neither of the apparent missiles had fallen within the waters of the country’s exclusive economic zone and that there had been no effect on Japan’s security.

The U.S. military did not immediately respond to a request for comment.

On Saturday, the North fired several rounds of unidentified short-range “projectiles” into the Sea of Japan. Those flew for a range of about 70 km to 200 km, the JCS said.

Acting U.S. Secretary of Defense Patrick Shanahan said during a congressional hearing Wednesday that Pyongyang had launched “rockets and missiles” — the first time the Pentagon has detailed what it believes was fired.

The North’s Foreign Ministry called those launches “regular and self-defensive,” state-run media reported Wednesday.

“The recent drill conducted by our army is nothing more than part of the regular military training, and it has neither targeted anyone nor led to an aggravation of the situation in the region,” an unidentified ministry spokesperson said in a statement to the official Korean Central News Agency.

But the spate of launches could undercut what U.S. President Donald Trump’s has repeatedly touted as his greatest accomplishment so far in the two countries’ nuclear talks: halting missile and nuclear tests.

Prior to the two recent launches, the North’s last known missile test came in November 2017, when it test-fired the Hwasong-15 intercontinental ballistic missile, which experts believe is capable of striking much, if not all, of the continental United States.

Pyongyang informally adopted a freeze on missile flight tests from then on, and in April last year declared a “suspension” of nuclear and long-range missile tests, but a short-range test would not violate that unilateral suspension.

The latest firing also came as officials from the United States and Japan were visiting South Korea, including U.S. Special Representative for North Korea Stephen Biegun, to explore ways to resume the deadlocked nuclear talks. It is Biegun’s first visit to Seoul since Trump’s February summit with Kim in Hanoi collapsed without a deal on rolling back Pyongyang’s nuclear program.

North Korean First Vice Foreign Minister Choe Son Hui, a key figure in the nuclear negotiations with the United States, warned late last month of an “undesired consequence” for the U.S. if Washington does not adjust its policy on North Korea’s denuclearization by an end-of-the-year deadline Kim has set.

While Choe did not elaborate as to what that consequence might mean, it could suggest a resumption of nuclear or missile tests by the North.Thursday and Saturday’s launches appeared to signal that Kim was working to escalate tensions in an attempt to gain leverage with Washington.