US ambassador, Linda Thomas-Greenfield (Getty Images)

The top US envoy to the United Nations will meet with South Korea's defense chief Monday as part of her trip to Seoul this week for talks to boost bilateral cooperation amid North Korean threats.

Ambassador Linda Thomas-Greenfield arrived in the country Sunday for a four-day visit, with plans to meet senior South Korean officials, including Defense Minister Shin Won-sik, to discuss cooperation in the UN Security Council.

The visit comes after Russia last month vetoed the UN's annual renewal of an expert panel monitoring the North's compliance with UN sanctions.

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

With the veto, the panel's mandate is set to expire April 30, a termination that observers say could chip away at international efforts to curb evolving North Korean nuclear and missile threats.

Thomas-Greenfield and South Korean officials are expected to discuss measures to ensure the continued reporting of the North's weapons proliferation and sanctions evasion activities.

She will also travel to the Demilitarized Zone separating the two Koreas, meet young North Korean defectors and speak with students at Ewha Womans University before heading to Japan on Wednesday.

It marks Thomas-Greenfield's first visit to Seoul, and the first trip by a US ambassador to the UN since 2016. (Yonhap)