North Korea carried out GPS jamming attacks on Friday and Saturday, an operation that affected several ships and dozens of civilian aircraft in South Korea, Seoul’s military said.

The jamming allegations come about a week after the North launched its most advanced and powerful solid-fuel ICBM, its first launch since it was accused of sending troops to help Russia fight Ukraine.

The South launched its own ballistic missile into the sea on Friday in a show of force meant to demonstrate its determination to respond to “any North Korean provocations”.

“North Korea conducted GPS jamming challenges in Haeju and Kaesong yesterday and today,” Seoul’s chiefs of staff said in a statement on Saturday, adding that several ships and dozens of civilian aircraft were experiencing “some operational disruptions “.

The military warned ships and aircraft operating in the Yellow Sea to beware of such attacks.

“We strongly urge North Korea to immediately cease GPS provocations and warn that it will be held accountable for any further problems arising from it,” they said in the statement.

Relations between the two Koreas are at one of their lowest points in years, with the North launching a series of ballistic missiles in violation of UN sanctions.

It has also been bombing the South with balloons carrying garbage since May in what it says is retaliation for anti-Pyongyang propaganda letters sent to the North by activists.

The South Korean military said Pyongyang also tried to jam GPS signals in May, but added at the time that it did not prevent any military operations in the south.

In Friday’s drill, South Korea fired a short-range Hyunmoo surface-to-air missile into the West Sea, which the military said would show Seoul’s “strong determination to respond firmly” to any North Korean threats.

The Hyunmoo missiles are key to the country’s so-called “Kill Chain” pre-emptive strike system, which allows Seoul to launch a strike if there are signs of an imminent North Korean attack.

Experts say such jamming attacks may lead to further incidents that could escalate tensions on the Korean peninsula.

“It remains unclear whether there is an intention to distract the world from the troop deployment, to instill psychological insecurity among residents in the South or to respond to Friday’s drills,” Yang Moo-jin, president of the University of North Korean Studies in Seoul, told AFP.

“However, GPS jamming attacks pose a real risk of serious incidents, including potential aviation accidents in the worst case scenario.”

Ahn Chan-il, a defector turned researcher who heads the World Institute for North Korean Studies, told AFP the North’s jamming could be “to protect its own communications and information exchanges during critical military operations”, both in the country as well as abroad.

North Korea has become one of the most vocal and important supporters of Russia’s offensive in Ukraine.

Seoul and the West have long accused Pyongyang of supplying artillery shells and missiles to Moscow for use in Ukraine.

The latest allegations, based on intelligence reports, indicate the North has deployed around 10,000 troops to Russia, suggesting an even deeper involvement in the conflict and sparking protests in Seoul, Kiev and Western capitals.

Seoul, a security ally of Washington, said last month that the presence of North Korean troops in Europe would be a major escalation.

South Korea, a major arms exporter, has a longstanding policy of not supplying weapons to countries in conflict.

But President Yoon Suk Yeol said this week that Seoul is now not ruling out supplying weapons directly to Ukraine, given Pyongyang’s military support for Moscow.

On Friday, the presidential office in Seoul said cyber attacks by pro-Russian hacking groups against South Korea had increased following North Korea’s deployment of troops to Russia’s war in Ukraine.