China’s top nuclear envoy Wu Dawei visited North Korea on Tuesday amid mounting calls for Beijing to raise pressure on Pyongyang to renounce its nuclear ambitions.

Wu landed at a Pyongyang airport in the afternoon, according to Kyodo News. The purpose of his visit was not immediately known.

Attention is focused on what kind of role China can play in curbing the growth of the North’s nuclear program and preventing its additional provocations. The North was seen preparing for a long-range rocket launch.

Wu’s visit to Pyongyang came amid ongoing efforts by Seoul, Washington and Tokyo to adopt a fresh U.N. Security Council resolution entailing stringent sanctions for the reclusive regime’s Jan. 6 nuclear test.

China has so far remain reluctant over the moves to adopt tougher sanctions against its recalcitrant ally, calling for caution and restraint. China has maintained that the nuclear issue should be settled through dialogue rather than a sanctions-centric approach.

However, the South, the U.S. and Japan have agreed to push for “strong and comprehensive” international sanctions, stressing that the world can no longer take a “business-as-usual” approach to the North’s latest provocation.

Despite China’s lukewarm response to what the North claims to be a hydrogen bomb test, the South has pressured China to play an “active role” in addressing the nuclear issue.

China is seen as having the greatest leverage over its wayward ally. Trade between the North and China accounts for some 90 percent of Pyongyang’s aggregate trade, with all its oil supplies imported from China.

By Song Sang-ho (sshluck@heraldcorp.com)