Lambert, who is on a three-day visit to Nepal, made this appeal to lawmakers, senior government officials and ruling Nepal Communist Party (NCP) co-chair Pushpa Kamal Dahal here on Friday, reports The Himalayan Times.
The envoy expressed concerns about growing business activities of North Koreans in Nepal.
"He also expressed fear that North Koreans might have been using Nepal as a base to commit cyber crimes," a lawmaker, who met Lambert, said.
Lambert's message during these meetings was clear - the UN Security Council has placed sanctions on North Korea, and Nepal, as a member country, should respect this decision.
The UN has imposed a number of sanctions on North Korea after the country started developing nuclear weapons, in violation of the UN charter. These sanctions, among others, bar UN member countries from hosting citizens of North Korea.
"Nepal is a member of the UN and it has the obligation to follow resolutions passed by the UN Security Council," said US Embassy Spokesperson Andie De Arment, who confirmed that Lambert was in Nepal to discuss growing activities of North Koreans in the country.
Earlier, US Secretary of State Mike Pampeo had also raised the North Korean issue during Foreign Minister Pradeep Kumar Gyawali's visit to the US last December.
( With inputs from IANS )