UNITED NATIONS/SEOUL (REUTERS) - The US ambassador to the United Nations, Nikki Haley, warned North Korea on Tuesday (Jan 2) against another missile test and said Washington would not take planned talks between North and South Korea seriously if Pyongyang did not take steps to give up its nuclear weapons.

Haley told reporters the United States was hearing reports that North Korea might be preparing to fire another test missile.

"We hear reports that North Korea might be preparing for another missile test," Haley said. "I hope that doesn't happen. But if it does, we must bring even tougher measures to bear against the North Korean regime."

South Korea on Tuesday offered talks with North Korea next week amid a standoff over its weapons programmes, a day after North Korean leader Kim Jong Un said he was open to negotiations but that his country would push ahead with "mass producing" nuclear warheads.

Tension has been rising over North Korea's nuclear and missile programmes, which it pursues in defiance of years of UN Security Council resolutions, with bellicose rhetoric coming from both Pyongyang and the White House. North Korea sees regular war drills between South Korea and the United States as preparations for war.

Kim said in a New Year's Day speech he was "open to dialogue" with Seoul, and for North Korean athletes to possibly take part in the Winter Games. He persistently declared North Korea a nuclear power.

Asked about the possibility of talks, Haley said: "We won't take any of the talks seriously if they don't do something to ban all nuclear weapons in North Korea."

"North Korea can talk to anyone they want, but the US is not going to recognise it or acknowledge it until they agree to ban the nuclear weapons that they have," she said.

Haley gave no details of the missile test preparations.

Another US official, who spoke on condition of anonymity, said there were indications that could point towards a potential missile launch "sooner rather than later," but cautioned that such signs had been seen in the past and no test had resulted.

US State Department spokeswoman Heather Nauert said North Korea might be "trying to drive a wedge of some sort" between the United States and South Korea and added that while it was up to Seoul to decide who it talked to: "We are very sceptical of Kim Jong Un's sincerity in sitting down and having talks."

US President Donald Trump, who has led a global drive to pressure North Korea to give up development of nuclear-tipped missiles capable of hitting the United States, held back judgment on Pyongyang's offer to talk, saying: "Perhaps that is good news, perhaps not - we will see!"

South Korea's Unification Minister Cho Myong-gyon said the offer for high-level talks next Tuesday had been discussed with the United States. A decision on whether to push back massive joint military drills until after the Winter Olympics which South Korea hosts next month is pending.

Cho suggested the talks be held at the border village of Panmunjom and said they should be focused on North Korea's participation at the Olympics, but other issues would likely arise, including the denuclearisation of North Korea.

"I repeat: The government is open to talking with North Korea, regardless of time, location and form," Cho said.

Should the talks be held, it would be the first such dialogue since a vice-ministerial meeting in December 2015.

This week's exchanges follow a year dominated by fiery threats from Kim and Trump, who warned that the United States would have no choice but to "totally destroy" North Korea if forced to defend itself or its allies, even as US diplomats pushed for a diplomatic solution.

North Korea regularly threatens to destroy the United States, South Korea and Japan and tested its most powerful intercontinental ballistic missile in November, which it said was capable of delivering a warhead anywhere in the United States.

Analysts see Kim's offer as an attempt to weaken the US-South Korean alliance and the US led campaign to raise pressure on Pyongyang through sanctions.

South Korean President Moon Jae-in welcomed Kim's address and asked his government to move as quickly as possible to bring North Korea to the Olympics, but he stressed that an improvement in inter-Korean relations "cannot go separately with resolving North Korea's nuclear programme".

Trump said sanctions and other pressures were starting to have a big impact on North Korea.

"Rocket man now wants to talk to South Korea for first time," he said on Twitter, using his nickname for Kim. "Perhaps that is good news, perhaps not - we will see!"

China, which has persistently urged a return to talks to ease tensions, said recent positive comments from North and South Korea were a good thing.

"China welcomes and supports North Korea and South Korea taking earnest efforts to treat this as an opportunity to improve mutual relations, promote the alleviation of the situation on the Korean peninsula and realise denuclearisation on the peninsula," Foreign Ministry spokesman Geng Shuang said.