Speaking to reporters Monday, Defense Secretary James Mattis said North Korea is "intentionally doing provocations that seem to press against the envelope for just how far can they push without going over some kind of a line in their minds that would make them vulnerable".
Following his speech at the UN, South Korean President Moon Jae-in will meet with his US counterpart to discuss North Korea's nuclear crisis amid escalating tensions over whether President Donald Trump's harsh rhetoric against North Korean leader Kim Jong-un could lead to a miscalculation.
The foreign ministry statement, carried by North Korea's official news agency KCNA, said: "The increased moves of the USA and its vassal forces to impose sanctions and pressure on the DPRK [Democratic People's Republic of Korea] will only increase our pace towards the ultimate completion of the state nuclear force". But the liberal-leaning government of President Moon Jae-in said it has no intention of requesting that the US bring back such weapons. Pyongyang sees the sanctions as an attempt to starve the country of fuel and income for its weapons programmes, as well as restrict oil imports and ban textile exports.
The fresh measures followed the sixth and most powerful nuclear test conducted by Pyongyang earlier this month.
Media captionHow would war with North Korea unfold?
But some critics have raised questions over the effectiveness of the restrictions, as North Korea continues to be able to trade internationally.
South Korea on Thursday approved a plan to provide $8 million in aid to North Korea via United Nations agencies as it seeks to handle humanitarian issues separately from political situations. The country's main partner is China and it is considered partially responsible for an estimated economic growth a year ago.
The US and North Korea leaders also exchanged threats of mutual destruction.
Four F-35B stealth fighters and two B-1B bombers staged "mock bombing drills" over the peninsula on Monday morning, South Korea's Yonhap news agency said, citing an unidentified Seoul government source.
An official directly familiar with options planning within the Trump administration told CNN the question that now needs to be answered is whether North Korea's missile program has progressed to the level of being such an inherent threat that the Pentagon would recommend targeting a missile even if its trajectory did not indicate it would hit the USA or its allies.
Separately, China and Russian Federation began a joint naval exercise east of the Korean peninsula.
While Spain is the latest country to uphold the recent set of sanctions drawn by the United Nations Security Council and the U.S., a list of nations in other continents have also been severing both diplomatic and economic ties with the North Korean regime.