Seoul, South Korea – North Korea fired a salvo of short-range ballistic missiles early Tuesday, Seoul's military said, Pyongyang's second launch in days and just hours before Americans vote for a new president.

Seoul's Joint Chiefs of Staff said it detected the launch of "several short-range ballistic missiles," at around 7:30 AM local time Tuesday into waters east of the Korean peninsula.

"In preparation for additional launches, our military has strengthened surveillance and alertness," it said, adding it was sharing information with Tokyo and Washington.

Tokyo also confirmed the launch, with the prime minister's office saying Pyongyang had "launched a suspected ballistic missile."

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On Thursday, the nuclear-armed North test-fired what it said was its most advanced and powerful solid-fuel intercontinental ballistic missile (ICBM). It was Kim Jong Un's first weapons test since being accused by the West of sending soldiers to Russia.

It also came just hours after US and South Korean defense chiefs called on Pyongyang to withdraw its troops, warning that North Korean soldiers in Russian uniforms were being deployed for possible action against Ukraine.

On Sunday, South Korea, Japan, and the United States conducted a joint air drill involving a heavy bomber in response to the ICBM launch.

The drill mobilised the US' B-1B bomber, South Korea's F-15Km and KF-16 fighter jets, and Japan's F-2 jets.

Such joint drills infuriate Pyongyang, which views them as rehearsals for invasion.

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Kim Yo Jong, sister of the country's leader and a key spokesperson, called the drill an "action-based explanation of the most hostile and dangerous aggressive nature of the enemy toward our Republic."

In a statement carried Tuesday by the official Korean Central News Agency, she said the drill was "absolute proof of the validity and urgency of the line of building up the nuclear forces we have opted for and put into practice."

She warned that any "upset of the balance of power between rivals on the Korean peninsula and in the region precisely means a war."

Experts have suggested the spate of weapons tests by Pyongyang could be a bid to distract attention from its purported troop deployment to Russia, or bump itself up the agenda ahead of the US election.

Seoul has long accused the nuclear-armed North of sending weapons to help Moscow fight Kyiv and alleged that Pyongyang has moved to deploy soldiers en mass in the wake of Kim Jong Un's signing of a mutual defense deal with Russian President Vladimir Putin in June.

It has also warned that Russia may be providing new technology or expertise in return for weapons and troops to help them fight Ukraine.

Seoul, a major weapons exporter, has said it is reviewing whether to send weapons directly to Ukraine in response, something it has previously resisted due to longstanding domestic policy that prevents it from providing weaponry into active conflicts.

North Korea has denied sending troops, but its vice foreign minister has said any such deployment would be in line with international law.