South Korea's top nuclear envoy arrived in Beijing on Wednesday for talks on ways to help bring North Korea back to the negotiating table, Seoul diplomats said, amid fresh signs of tension as the North appears to be preparing to launch a long-range rocket.
  

Hwang Joon-kook, South Korea's special representative for Korean Peninsula peace and security affairs, is scheduled to meet with his Chinese counterpart, Wu Dawei, on Thursday, diplomats said.
  

Earlier in the day, a South Korean government source told Yonhap News Agency that North Korea has erected a 67-meter launch tower at its missile base on the west coast, in an apparent preparation to launch a long-range rocket, possibly in October.
  

North Korea, which is banned for conducting any ballistic missile and nuclear tests under U.N. resolutions, will mark the 70th anniversary of the founding of its ruling Workers' Party on Oct. 10.
  

Hwang is also expected to ask Wu to exercise more leverage over North Korea to break a long-running impasse in the North Korean nuclear negotiations, a South Korean diplomat said on the condition of anonymity.
  

"Given North Korea's rejection of dialogue on its nuclear program, it is all the more necessary to deepen strategic communications with China on the North Korean nuclear issue," the diplomat said.
  

Last week, the United States, five world powers and Iran reached the landmark deal that will curb Iran's nuclear capabilities in return for lifting sanctions.
  

In its first official response to the Iran deal, North Korea said Tuesday that it was not interested in Iran-style nuclear talks, adding it has already become a nuclear weapons state.
  

North Korea, which conducted its third and most powerful nuclear test in 2013, has a track record of starting a crisis, coming to negotiations and reaching an agreement in exchange for economic and other concessions, then ditching the deal.
  

Mindful of the North's behavior, South Korea and the U.S. have called for Pyongyang to demonstrate its commitment to denuclearization through actions before the six-party talks can resume. Diplomatic efforts by China, North Korea's long-time ally, have still been seen as more accommodating toward Pyongyang.
  

The multilateral talks grouping the two Koreas, the U.S., China, Japan and Russia have been at a standstill since late 2008. (Yonhap)