Ri Yong-ho told the UN General Assembly the sanctions were deepening North Korean mistrust of the US.
"Without any trust in the USA there will be no confidence in our national security and under such circumstances there is no way we will unilaterally disarm ourselves first", Ri said.
"Without any trust in the United States, there will be no confidence in our national security and under such circumstances, there is no way we will unilaterally disarm ourselves first".
President Trump told supporters on Saturday night that he and North Korean dictator Kim Jong-un "fell in love" in the process of setting up the failed peace summit the two leaders attended in Singapore earlier this year.
Before they turned the page on decades of public acrimony, the leaders regularly traded threats and insults as North Korea pushed to develop a nuclear missile capable of hitting the US.
"The perception that sanctions can bring us on our knees is a pipe dream of the people who are ignorant about us", he added.
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I yelled, hoping that someone downstairs might hear me and I tried to get away from him but his weight was heavy", she said. "It was hard for me to breathe, and I thought Brett was accidentally going to kill me", her testimony says.
Mr Trump was likely referring to the letters he received from Mr Kim that his White House spokeswoman Sarah Sanders described at the time as "a very warm, very positive letter."
Donald Trump has said that he and Kim Jong-un "fell in love" after writing "beautiful letters" to each other. "And we would go back and forth", Trump said at a rally in West Virginia.
Last week, US Secretary of State Mike Pompeo said he would return to Pyongyang in October to prepare for a follow-up Trump-Kim summit.
The crowd laughed in response to Trump's "love" line, though the comment was more self aggrandizement than humor - he had also just informed supporters that he had prevented the deaths of millions, come up with a better foreign policy toward the rogue nation than President Obama or any other US leader, and that anyone who says any different is lying. "Am I allowed to say that?"
It added that the United States is only intent on keeping sanctions in place without holding up its end of the bargain amid a mood of detente on the Korean Peninsula.