North Korea on Friday denounced the recent visit to South Korea and Japan by the top US envoy to the United Nations, calling it an "aid-begging" trip to invigorate the "weakened illegal" sanctions against Pyongyang.

Late last month, the UN Security Council failed to extend the mandate of the panel of experts monitoring the enforcement of sanctions against the North's nuclear and missile programs due to Russia's veto. The operation of the panel is set to expire on April 30.

Ambassador Linda Thomas-Greenfield made a four-day trip to South Korea before traveling to Japan on Thursday in an apparent move to seek an alternative to the UN monitoring panel.

Kim Son-gyong, North Korea's vice foreign minister in charge of international organizations, said Thomas-Greenfield is making the last-ditch effort to continue to "beat the drum of pressure by sewing up a ripped sanctions drum" but will only meet with cold treatment and derision from the international community.

Her trip is "no more than an aid-begging trip of a loser to enliven the weakened illegal sanctions and pressure on the DPRK with the help of inferior allies," Kim said in a statement carried by the North's official Korean Central News Agency, referring to North Korea's official name, the Democratic People's Republic of Korea.

North Korea has been under tightened UN sanctions due to its nuclear and missile programs, which call for, among other things, a ban on the country's exports of coal and other mineral resources to cut off its access to hard currency.

During a visit to the Demilitarized Zone separating the two Koreas on Tuesday, Thomas-Greenfield said the US is looking at "out of the box" options with South Korea and others to continue the sanctions monitoring on North Korea. (Yonhap)