GENEVA • The United Nations Security Council has met behind closed doors to discuss tightening sanctions on North Korea after it fired its latest ballistic missile.

US Ambassador Nikki Haley said the United States was working with China, the North's main ally, on a new sanctions resolution and warned that all countries must step up action against North Korea or face measures themselves.

"We all have to send a sign to North Korea, and that is 'No more. This is not play time. This is serious. These threats are not welcome'," Ms Haley said ahead of the meeting.

"If you are a country that is supplying or supporting North Korea, we will call you out on it," she said. "We will make sure that everyone knows who you are and we will target those sanctions towards you as well."

Despite the push for a tougher stance, she held out the prospect of direct talks with North Korea, saying "we are willing to talk but not until we see a total stop of the nuclear process and of any test there".

On Sunday, North Korea launched what appeared to be its longest-range ballistic missile yet, saying it was capable of carrying a "heavy nuclear warhead" in a test aimed at bringing the US mainland within reach.

The US, Japan and South Korea called the emergency meeting to press international demands that North Korea change course and dismantle its missile and nuclear programmes. No draft resolution was circulated to the full council, but Ms Haley said the US is working with China on a text.

"That's what we are working on now. We don't have it done yet," Ms Haley said. "Absolutely, sanctions (are) something that we are looking at and we are going to continue to see where that takes us."

However, during the closed-door meeting, China made no mention of a new sanctions resolution and renewed its appeal for talks to ease tensions on the Korean peninsula, according to diplomats.

After the meeting, the council president, Uruguay's Ambassador Elbio Rosselli, said that "clearly sanctions are a way to go", but stressed support for diplomacy to engage with Pyongyang.

North Korea has carried out two atomic tests and dozens of missile launches since the beginning of last year, in its quest to develop a missile capable of delivering a nuclear warhead to the continental US.

In a unanimous statement backed by China, the council on Monday agreed to take further significant measures, including sanctions. Among the possible measures could be an oil embargo, trade bans and targeted sanctions on North Korean individuals and companies, but these hinge on China's willingness to apply such measures.

The Security Council adopted two sanctions resolutions last year to ramp up pressure on Pyongyang and deny leader Kim Jong Un the hard currency needed to fund his military programmes.

In all, six sets of sanctions have been imposed on North Korea since it first tested an atomic device in 2006. Under UN resolutions, North Korea is barred from developing nuclear and missile technology.

In Washington, a US defence official said the missile fired on Sunday appeared to be a liquid-fuelled KN-17, marking what seemed to be the most successful launch of such a device. But the Pentagon is sceptical whether Pyongyang has mastered the re-entry technology needed to ensure the missile survives returning into Earth's atmosphere.

The rocket, which Pyongyang dubbed the Hwasong-12, marks a significant milestone in its development of an intercontinental ballistic missile that could be tipped with a nuclear warhead, experts said.

AGENCE FRANCE-PRESSE