North Korea on Tuesday fired short-range ballistic missiles into the sea east of the Korean Peninsula, hours before the US goes to the polls to elect its next president.

The South Korean Joint Chiefs of Staff said in a brief announcement the missiles were launched at around 7:30 a.m. from a province south of Pyongyang and traveled 400 kilometers before landing in the waters.

South Korean and US military and intelligence officials are analyzing details of the launch, including their type and range.

Yang Uk, a research fellow at Asan Institute for Policy Studies in Seoul, told The Korea Herald the missiles appear to have been fired using the 600 mm “super-large” multiple rocket launchers.

“North Korea seems to be using the new 600 mm multiple rocket launchers for firing short-range missiles recently instead of the Hwasong family of short-range ballistic missiles, KN-23 and KN-24,” he said.

According to the National Intelligence Service, North Korea is believed to have provided Russia with KN-23 missiles, which were used to strike Ukraine.

Kim Yo-jong, the sister of North Korean leader Kim Jong-un, on Tuesday slammed the US flying its B-1B bombers in a trilateral air drill with South Korea and Japan near the Korean Peninsula on Sunday as “acts of utmost hostility.”

She said the air training, the second to be held by South Korea, US and Japan this year, “serves as a justification” for expanding the country’s nuclear program.

“This year alone, the US and its minions have staged dozens of war games mimicking the use of nuclear weapons against us, and carried out more than a hundred anti-Democratic People’s Republic of Korea military exercises,” she said, using North Korea’s official name.

Among “anti-Pyongyang military exercises” cited by Kim were the South Korea-US-Japan multidomain exercise Freedom Edge and the South Korea-US tabletop exercise Iron Mace.

“It is an undeniable reality that the destruction of the balance of power on the Korean peninsula and in the region would mean war,” she said.

On the missile firings by North Korea, the South Korean military said Pyongyang was “isolating itself from the international community” by staging provocations and blowing up inter-Korean roads.

“North Korea is turning itself into a harsh prison camp,” the South’s JCS said in a brief statement. The launches of ballistic missiles in particular were illegal and violations of the United Nations Security Council Resolutions, it said.

The last time North Korea fired a ballistic missile was Thursday, when it tested what was suspected to be a new intercontinental ballistic missile that may be capable of reaching the US. The new missile flew higher and longer than any missile North Korea had tested in the past.

South Korean military and intelligence officials warned last week of signs of North Korea preparing to stage a large-scale provocation such as a nuclear test or an ICBM firing around the time of the US election.