North Korea fired two short-range ballistic missiles on Wednesday, Seoul’s military said, just days after Pyongyang’s last test and ahead of a visit to South Korea by US Vice President Kamala Harris.

The launches, which were part of a record-breaking blast of weapons tests by North Korea this year, came after Seoul’s spy agency warned that Pyongyang was close to conducting another nuclear test.

South Korea’s military said it had “detected two short-range ballistic missiles fired from the Sunan area of ??Pyongyang.”

The missiles flew “about 360 kilometers (223 miles) at an altitude of 30 kilometers at a speed of Mach 6,” Seoul’s Joint Chiefs of Staff said in a statement, adding that they were analyzing the details of the launches.

“Our military has increased surveillance and surveillance and maintains the greatest preparedness in close coordination with the United States,” he added.

Japan also confirmed the launches, with Deputy Defense Minister Toshiro Ino saying North Korea’s recent spate of missile tests was “unprecedented” in frequency.

“The repeated rocket launches cannot be tolerated,” he said.

The latest launch came after North Korea tested a short-range ballistic missile on Sunday.

Harris will arrive in Seoul on Thursday for a brief visit during which she will visit the heavily fortified border between North and South Korea.

The White House said Harris’ trip, which follows a visit to Japan, was intended to underscore the importance of the alliance with Seoul.

Washington is Seoul’s main security ally, stationing about 28,500 troops in South Korea to protect it from the North.

Last week, the nuclear-powered USS Ronald Reagan conducted joint drills with the South Korean Navy in waters off the Korean peninsula.

Under Seoul’s fiercely new President Yoon Suk-yeol, who took office in May, the two countries have stepped up joint drills they claim are purely defensive — but North Korea sees them as rehearsals for an invasion.

South Korean and US officials have been warning for months that North Korean leader Kim Jong Un is preparing for another nuclear test.

Earlier Wednesday, Seoul’s spy agency said Pyongyang appears to have “completed a third tunnel at its Punggye-ri nuclear site,” MP Yoo Sang-bum told reporters after a Seoul National Intelligence Service briefing.

Pyongyang is likely to choose the window between “China’s upcoming Communist Party Congress on Oct. 16 and the United States’ mid-term elections on Nov. 7” for its next nuclear test, Yoo said.

North Korea, under multiple UN sanctions over its weapons programs, typically seeks to maximize the geopolitical impact of its tests through careful timing.

The isolated regime has tested nuclear weapons six times since 2006. The latest and most powerful, in 2017 – which Pyongyang dubbed a hydrogen bomb – had an estimated yield of 250 kilotons.

Seoul has also spotted signs the North is preparing to launch a submarine-launched ballistic missile (SLBM), the president’s office said Saturday, a weapon Pyongyang last tested in May.

“Today’s launch makes it clear that the North is trying to gain the upper hand on the peninsula with a nuclear arsenal at its disposal,” Kim Jong-dae of the Yonsei Institute for North Korean Studies told AFP.

The repeated tests are “a harbinger of Pyongyang’s aggressive stance to come next month — with missile launches and a possible nuclear test,” he said.