North Korea said Sunday it had carried out a "very important test" at its space launch centre, as Pyongyang ramps up pressure on Washington over stalled nuclear talks.

The announcement of Saturday's test at the Sohae satellite launch site came just hours after US President Donald Trump said he'd be "surprised" by any hostile action from the North.

"A very important test took place at the Sohae Satellite Launching Ground on the afternoon of December 7, 2019," a spokesman for North Korea's Academy of the National Defence Science said.

The result of the latest test will have an "important effect" on changing the "strategic position" of North Korea, the spokesman said in a statement carried by the KCNA news agency.

The statement did not provide further details on the test.

Satellite imagery taken on December 5 showed a large container box at the site that was "a decent indicator of an impending engine test", Jeffrey Lewis of the US-based Middlebury Institute of International Studies had said ahead of Pyongyang's statement.

Sohae, on North Korea's northwest coast, is ostensibly a facility designed for putting satellites into orbit.

But Pyongyang has carried out several rocket launches there that were condemned by the US and others as disguised long-range ballistic missile tests.

Rocket engines are easily repurposed for use in missiles and the international community has called Pyongyang's space programme a fig leaf for weapons tests.

North Korea dismantled the test stand at Sohae amid a rapid rapprochement in 2018 but reassembled it this year, Lewis said, adding, "Still, we had not seen any activity at the test stand" until now.

"It is clear that this is one more sign that North Korea is conducting more missile-related activities as Kim Jong Un's end-of-year deadline for sanctions relief approaches," he said, referring to the North Korean leader.

End-of-year deadline

The latest test comes as Pyongyang is ramping up pressure ahead of its December 31 deadline for the US to propose a new offer to kickstart stalled nuclear talks.

Hours before North Korea announced its latest test, Trump had emphasised his "very good relationship" with Kim.

"Well, we'll see about North Korea. I'd be surprised if North Korea acted hostiley," he said on Saturday afternoon in Washington DC.

"(Kim) knows I have an election coming up. I don't think he wants to interfere with that. But we'll have to see."

Following his first summit with Kim in June 2018, Trump said Kim had agreed to destroy "a major missile engine testing site" without naming the facility.

Kim then agreed to shutter the Sohae site during a summit last year with South Korean President Moon Jae-in in Pyongyang as part of trust-building measures.

Kim has held three meetings with Trump since June 2018 but little progress has been made in efforts towards denuclearisation.

On Thursday, the North's vice foreign minister warned of returning to a war of words with the US, threatening to resume referring to Trump as a "dotard" -- Pyongyang's nickname for the US leader at the height of tensions in 2017.

The comments came a day after it warned that if the US used military force against the North it would take "prompt corresponding actions at any level".

At the recent NATO summit, Trump boasted about Washington's "most powerful military", adding: "Hopefully, we don't have to use it, but if we do, we'll use it. If we have to, we'll do it."