A secret envoy sent by North Korea's young leader Kim Jong-un recently paid a visit to Beijing with a mission to "figure out the feelings of the Chinese leadership" and "gauge the level of possible sanctions by the US and South Korea" if the North carries out a third nuclear test, South Korea's JoongAng Ilbo newspaper reported on Thursday, citing an unidentified source.

The report said that the envoy, an official of the ruling Workers' Party's international affairs department, arrived in Beijing on Wednesday, without stating the specific identification.

Yu Shaohua, a researcher with the China Institute of International Studies, said it was hard to verify the information because previous visits by North Korean leaders and high-level officials to China were usually kept secret before they traveled back to their country.

If true, it would be the first North Korean envoy dispatched to China after the UN Security Council passed Resolution 2087 in late January deploring the North's defiant rocket launch last December.

"We assume that Pyongyang intends to explain its position on the alleged nuclear test plan and figure out the feeling in the Chinese leadership over the matter," the source in Beijing told JoongAng Ilbo. "They could try to gauge the level of possible sanctions that Seoul and Washington are mulling to take against the regime."

Zhang Tuosheng, an expert with the China Foundation for International and Strategic Studies, said Pyongyang appeared "quite different" this time after it declared it would carry out a fresh nuclear test.

"The first and second nuclear tests came very soon after its announcements, but the third one, although hard to avert, is taking a much longer time to happen," Zhang said. "North Korea is probably attempting to draw attention by appearing to 'hesitate' over its decision."

North Korea was testing the bottom line of each regional player during the "hesitation period" as it has "very limited cards to play," Yu said.

"Anything is possible during this sensitive period," Yu told the Global Times.

South Korea's Finance Ministry confirmed on Thursday that it would impose the necessary restrictions from next week on the same North Korean personnel and organizations named by the UN resolution, despite dire warnings by the North over the consequences.

The US and South Korea were also reportedly engaged in talks on separate joint sanctions, including a possible "sea blockade," in addition to existing ones imposed by the UN against the North.

A spokesman for North Korea's National Economic Cooperation Committee warned that the North may shut down the Kaesong Industrial Complex, a symbolic joint industrial zone between the two Koreas, if South Korea links the project to sanctions.

North Korea will withdraw all privileges for Kaesong and restore the area as a military zone, the spokesman said in a statement carried by the North's official Korean Central News Agency.

Separately, in an apparent response to the North's surprising development in long-range missile technology, South Korea's navy chief said on Thursday that in the next couple of years all its warships will complete deployment of land-attack missiles that are able to hit all parts of North Korea.

The US last October allowed South Korea to extend its missile range from 300 kilometers to 800 kilometers following the North's failed attempt to launch a long-range rocket in April.

Pyongyang said on Wednesday that its response to the hostility of Seoul and Washington would be "beyond imagination."

Agencies contributed to this story