Pyongyang, North Korea - North Korea on Friday ridiculed this week's Asia tour by the top US envoy to the United Nations, calling it the "aid-begging trip of a loser".

Linda Thomas-Greenfield on Tuesday urged Pyongyang to return to dialogue during a visit to South Korea, adding later she still believed sanctions were an "effective tool" to deter the nuclear-armed North.

Her comments followed Russia last month using its UN Security Council veto to effectively end UN monitoring of violations of the raft of sanctions on Kim Jong-un's regime.

In a statement, Pyongyang's foreign ministry said Thomas-Greenfield's trip – which began Sunday, a day after Iran's drone and missile strike on Israel – would have been better spent addressing the spiraling situation in the Middle East.

"The US has taken no account of peace and security guarantee in the Middle East including Palestine, but it is at a loss for the miserable fate of the tattered sanctions mechanism against the DPRK," said the statement signed by vice-minister Kim Son Gyong.

The US envoy's tour of the region was "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," it added.

Last year, North Korea conducted a record number of missile tests in defiance of UN sanctions in place since 2006 and despite warnings from Washington and Seoul, having enshrined its status as a nuclear state in its constitution.

During her stay in Seoul, Thomas-Greenfield blamed countries including "Russia and Iran" for having "not implemented these sanctions" against the North "in a way that will allow them to work as effectively as they can".

She also said Washington was collaborating with Seoul, Tokyo, and others to explore "some creative ways" and "out-of-the-box thinking" to ensure the continuation of the UN's monitoring activities.

But North Korea said the US envoy appeared to have "forgotten her duty," a day after the US caused widespread outrage by using its Security Council veto to block full Palestinian membership at the UN.

"At present, the Middle East situation, including Palestine's admission to a UN membership, is brought up for discussion at the UNSC as the most pressing issue," Pyongyang's statement said.

The US has repeatedly paid lip service to a two-state solution to the Palestinian-Israeli conflict, but in practice, any and all progress is conditioned by Israel's unilateral approval.