South Korea has sanctioned eight people and seven companies suspected of engaging in illicit activities to finance North Korea’s growing nuclear weapons and missile programmes.

The move, which prohibits South Koreans from conducting any type of business with them without authorisation, was largely symbolic as there are little financial dealings between the rival Koreas.

But the steps may still draw an irritated response from North Korea, which last month called South Korean President Yoon Suk Yeol and his government “idiots” and a “wild dog gnawing on a bone given by the US” after Seoul said it is considering placing more unilateral sanctions on Pyongyang.

The South Korean sanctions were announced shortly after the US Treasury Department said it sanctioned three members of North Korea’s ruling Workers’ Party who provided support to the country’s development of nuclear and ballistic weapons.

South Korea’s foreign ministry said Seoul’s sanctions were in response to the North’s heightening weapons threat, highlighted by last month’s testing of an intercontinental ballistic missile that demonstrated potential range to reach the US mainland.

The eight people and seven companies targeted by Seoul had already been sanctioned by Washington and were involved in a variety of North Korean efforts to evade United Nations Security Council sanctions to finance its weapons programme, including ship-to-ship transfers of fuel and illicit exports of labour, the ministry said.

Those listed on the sanctions included six officials from four different North Korean banks, a Taiwanese national named Chen Shih Huan, and a Singaporean named Kwek Kee Seung.

Four of the sanctioned companies were North Korean trade and shipping firms and the other three were Singapore-based shipping firms.

The ministry said in a statement: “(Our) government has been maintaining close coordination with the United States and Japan so that the same individuals and groups are placed together under the unilateral sanctions of related nations to raise the awareness of the international community and strengthen the effectiveness of sanctions.”

South Korea imposed sanctions in October on 15 individuals and 16 organisations accused of supporting North Korea’s arms development, which were Seoul’s first unilateral sanctions on Pyongyang in five years.

North Korea ramped up its weapons demonstrations to a record pace this year, test-firing dozens of missiles including ICBMs, as it exploited the distraction created by Russia’s war on Ukraine to advance its weapons program and dial up pressure on Washington and Seoul.

US and South Korean officials have also said there are signs that the North is preparing to conduct its first nuclear test since September 2017.

That would escalate a brinkmanship experts say is aimed at forcing the United States to accept the idea of the North as a nuclear power, and negotiating concessions from a position of strength.

China and Russia vetoed a US-led attempt in May to toughen Security Council sanctions on North Korea over its earlier ballistic tests, underlining a division between the council’s permanent members deepened over Russia’s invasion of Ukraine.

Experts say the North’s next nuclear test, which would be its seventh overall, is likely be the first in which the Security Council fails to respond with new punitive measures.