North Korea says it's ready to give the United States a "severe lesson" with its strategic nuclear force if it takes military action against it, and will not put its nuclear program or its missiles on the negotiating table.

In a transcript of a statement by Foreign Minister Ri Yong-ho, which was distributed at the Association of South-East Asian Nations (ASEAN) forum in Manila, Pyongyang called the new UN sanctions "fabricated".

"We will under no circumstances put the nukes and ballistic rockets on (the) negotiating table," Ri told Asia's largest security forum.

"Neither shall we flinch even an inch from the road to bolstering up the nuclear forces chosen by ourselves unless the hostile policy and nuclear threat of the US against North Korea is fundamentally eliminated."

US President Donald Trump says he's spoken with South Korean President Moon Jae-in (AP Photo/Evan Vucci, File).

He warned there would be "strong follow-up measures" and acts of justice and said the resolution showed the United Nations had abused its authority.

It said its intercontinental ballistic missile tests in July proved that the entire United States was in its firing range, and those missiles were a legitimate means of self-defence.

It was not immediately clear whether the statement was read to the ASEAN forum on Monday.

Earlier North Korea said in a statement it would launch "thousands-fold" revenge against the US over the sanctions.

"There is no bigger mistake than the United States believing that its land is safe across the ocean," it said.

The UN Security Council unanimously imposed new sanctions on Saturday aimed at pressuring Pyongyang to end its nuclear program. The sanctions could slash North Korea's $US3 billion ($A3.8 billion) annual export revenue by a third.

The US-drafted resolution bans North Korean exports of coal, iron, iron ore, lead, lead ore and seafood following Pyongyang's two intercontinental ballistic missile tests in July.

It also prohibits countries from increasing the current numbers of North Korean labourers working abroad, bans new joint ventures any any new investment in current joint ventures.

During an hour-long phone call on Monday, South Korean President Moon Jae-in and US President Donald Trump vowed to continue co-operating to rein in North Korea, particularly ahead of a regular joint military drill set for late August, South Korean presidential office spokesman Park Su-hyun said.

Moon was also cited as saying there was a need to show North Korea dialogue is still open, should Pyongyang give up its nuclear program.

In a separate statement, the White House said the two leaders "affirmed that North Korea poses a grave and growing direct threat to the United States, South Korea, and Japan, as well as to most countries around the world".

"The leaders committed to fully implement all relevant resolutions and to urge the international community to do so as well," the White House said.

Trump tweeted that he was "very happy and impressed with 15-0 United Nations vote" on the sanctions.

North Korea has accused the US and South Korea of escalating tensions by conducting military drills.