The United States would consider talks with North Korea if it halts all nuclear and ballistic missile tests, Washington's envoy to the United Nations said on Tuesday, as the UN Security Council weighed new sanctions on Pyongyang.

"We are willing to talk but not until we see a total stop of the nuclear process and of any test there," the US envoy Nikki Haley told reporters ahead of a closed-door Security Council meeting.

Washington and Beijing - the North's sole diplomatic and military ally - are working on a new resolution targeting Pyongyang, she added.

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

READ MORE: North Korea says new rocket can carry nuclear warhead

On Sunday, North Korea launched what appeared to be the longest-range missile it has ever successfully tested, sparking global alarm.

Pyongyang said the missile, the Hwasong-12, was capable of carrying a "heavy nuclear warhead".

The reclusive North, which has defied all calls to rein in its weapons programmes - even from China - said the missile test was a legitimate defence against US hostility.

Under UN resolutions, North Korea is barred from developing nuclear and missile technology and the Security Council has repeatedly described Pyongyang's actions as provocative and a threat to global peace.

The missile, launched on an unusually high trajectory, flew to an altitude of 2,111.5km, and travelled 787km before landing in the Sea of Japan.

That suggests a range of 4,500km or more if flown for maximum distance, analysts said.

North Korea's missile programme is progressing faster than expected, South Korea's defence minister said on Tuesday.

Han Min-koo told South Korea's parliament the test-launch had been detected by the controversial American THAAD anti-missile system, whose deployment in the South has infuriated China.

Han said Sunday's test-launch was "successful in flight".

READ MORE: North Korea open to US talks under 'right conditions'

"It is considered an IRBM [intermediate range ballistic missile] of enhanced caliber compared to Musudan missiles that have continually failed," he said, referring to a class of missile designed to travel up to 3,000km to 4,000km.

Asked if North Korea's missile programme was developing faster than the South had expected, he said: "Yes."

The test-launch was a legitimate act of self-defence and US criticism was a "wanton violation of the sovereignty and dignity of the DPRK", a North Korean diplomat told the UN Conference on Disarmament in Geneva on Tuesday, using the initials for the country's official name, Democratic People's Republic of Korea.

US President Donald Trump warned in an interview with Reuters news agency this month a "major, major conflict" with North Korea was possible. In a show of force, the United States sent an aircraft carrier strike group, led by the Carl Vinson, to waters off the Korean peninsula to conduct drills with South Korea and Japan.