“We are living in the reality where there is a high possibility of military clashes” along the disputed sea border off the Koreas’ west coast or along the heavily fortified land frontier that divides them, Moon said.

The president made his remarks after his country’s unification ministry suggested talks with the North should resume.

“Our most basic stance is that communication lines between South and North Korea should open,” said Lee Duk-haeng, a spokesman for the ministry. “The unification ministry has considered options on this internally but nothing has been decided yet.”

Moon favours engagement with the North to bring it to the negotiating table, but after Sunday’s missile launch said dialogue would be possible “only if Pyongyang changes its behaviour”.

The North claimed the rocket was capable of carrying a nuclear warhead, although there are doubts whether the country could build a warhead small enough to fit into a missile.

The growing threats from the North prompted Seoul to recently deploy a powerful US anti-missile system despite angry opposition from China.

Nikki Haley, the US ambassador to the UN, said on Tuesday she was working with China, South Korea and Japan on new sanctions against North Korea.

“No one is immune to the threat of North Korea,” she told reporters before emergency closed-door consultations by the UN Security Council on the North’s weekend ballistic missile launch, which experts said demonstrated a significant technological jump with the rocket flying higher and for a longer period of time.

Haley said the US and China have been working on “a unified plan” on how to approach North Korea that would include tougher new sanctions.

She indicated Washington and Beijing had agreed they would take action if a new test looked to be long range and leaning toward an intercontinental ballistic missile that could reach the United States.

The latest launch appeared to fulfil both criteria, Haley said, “so I believe that China will stay true to that and that we’ll come together on how we’re going to do that.”

“We’re not going to continue to just say go ahead and test as often as you want,” Haley said, flanked by the South Korean and Japanese ambassadors. “This is a true threat to every country in the world. ... We’re going to make sure we put the pressure on them economically, diplomatically, politically and internationally.”

“[The US is] looking at third-country entities who are helping North Korea and putting sanctions on them because if you are supporting North Korea you are against the rest of the international community,” Haley said.

“We’re not going to continue to just say go ahead and test as ­often as you want. This is a true threat to every country in the world ... We’re going to make sure we put the pressure on them economically, diplomatically, politically and internationally.”

She indicated Washington and Beijing had agreed they would take action if a new test looked to be long range and suggested an intercontinental ballistic missile that could reach the US.

Chinese foreign ministry spokeswoman Hua Chunying (華春瑩) said yesterday all discussion and actions by the UN Security Council should aim to achieve a peaceful solution.

“China will continue to fully implement relevant UNSC resolutions,” she said at a briefing in Beijing. “As a permanent member of the UN Security Council and neighbour of Korean Peninsula, China ... will play a constructive role to ease the tension, lower the temperature, push all parties back to dialogue and consultation, and ultimately reach a proper settlement of the nuclear issue.”

Additional reporting by Robert Delaney, Zhenhua Lu