North Korea on Monday condemned the United Nations Security Council's fresh sanctions over its long-range missile tests, vowing to retaliate against the US with bigger actions.

North Korea warned in a statement that it is ready to use any ultimate means if the US does not give up its moves to stifle Pyongyang, according to the Korean Central News Agency.

"We are ready to respond with far bigger actions to make the US pay a price for its violent crime against our country and people," it said, vowing to take a "stern action of justice" as it earlier warned.

The UNSC on Saturday adopted fresh sanctions on North Korea following its two tests of intercontinental ballistic missiles in July.

The measures, including a ban on all exports of coal, are aimed at slashing the North's annual export revenue of $3 billion by a third. The sanctions resolution marked the eighth of its kind since 2006 when the North conducted its first nuclear test.

North Korea fired its first ICBM on July 4, followed by the launch of a similar missile that went a longer distance. It claimed that the whole US mainland is within its striking range.

North Korea reiterated that it will not put its nuclear weapons on the negotiation table, pledging to stick to its signature policy of seeking nuclear armament and economic development, commonly known as the byongjin policy.

The North's reaction came in the midst of an Asian security forum being held in Manila, which brought together 27 top diplomats from Asia and other regions including South and North Korea, the US and China.

The foreign ministers from South Korea, the US and Japan reaffirmed commitment to fully implement the latest U.N. sanctions, stressing firm three-way coordination in handling North Korea's nuclear and missile issue.

President Moon Jae-in took office in May with vows to take a dual-track approach of seeking sanctions and dialogue. The South earlier offered to hold military and family reunions talks to the North, but Pyongyang has kept mum toward the overture.

North Korea has claimed that its development of nuclear weapons is a deterrent against what it called Washington's hostile policy toward it.

"If enemies believe that North Korea can be rattled by sanctions, it is nothing more than a delusion," the statement showed. "As long as the US sticks to its hostile policy and nuclear blackmailing... we will not budge an inch from our path toward strengthening our nuclear force." 

Experts said that North Korea may carry out its sixth nuclear test or launch ballistic missiles including those launched from a submarine.

"I think that North Korea may declare 2018, the 70th anniversary of the regime's establishment, as the year of its accomplishment of nuclear force," said Chung Sung-yoon, a research fellow at the Korea Institute for National Unification. "The North could conduct a boosted fission nuclear weapon test with more explosive power."

Tensions on the divided Korean Peninsula are likely to further rise late this month as North Korea will likely show an angry reaction to an annual joint military drill between Seoul and Washington.

The North has claimed that the exercise is a rehearsal for their northern invasion, despite reassurances by the South and the US that it is defensive in nature.

Some experts said that the relevant parties would eventually sit down for dialogue after the North's provocative acts jack up the level of tensions.

US Secretary of State Rex Tillerson said Monday in Manila that North Korea's possible end to missile launches would be the "first and strongest signal" indicating the North is prepared for negotiations, according to foreign reports. (Yonhap)