BANGKOK (Reuters) - The chief U.S. negotiator for North Korea said on Friday the United States should engage in direct diplomacy with Pyongyang alongside sanctions imposed over its nuclear and ballistic missile programmes. U.S. Secretary of State Rex Tillerson offered on Tuesday to begin direct talks with North Korea without pre-conditions, but the White House later said no negotiations could be held until North Korea improved its behaviour.   We should exercise direct diplomacy as well as sanctions. That is our policy, which is based on pressure and engagement, and we do want to engage in pressure and diplomacy,  Joseph Yun, U.S. Special Representative for North Korea Policy, told reporters in Bangkok. Yun travelled to Japan and Thailand this week to meet officials to discuss ways to build pressure on North Korea after its latest ballistic missile test. On Thursday, Yun met the head of Thailand s National Security Council, General Wallop Rohsanoh, and deputy foreign minister Weerasak Futrakul.  We had very constructive, open-ended discussion,  said Yun. The United States had  no specific requests  for Thailand, he said. Thailand s Prime Minister Prayuth Chan-ocha said on Tuesday no trade takes place between Thailand and North Korea and that Thailand has abided by United Nations resolutions regarding North Korea.  We had no specific requests ... It seems like, as the deputy foreign minister said, they are fully complying with United Nations resolutions,  Yun told reporters.  Thailand s ties with North Korea have been in the spotlight this year. Tillerson pressed Thailand, the United States  oldest ally in Asia, for more action on North Korea during a visit to Bangkok in August. North Korea has an embassy in the Thai capital, Bangkok. Despite Tillerson s call for talks with Pyongyang without pre-conditions, the White House said now was not the right time and that any negotiations would have to be about giving up its nuclear arsenal.  I think what Secretary Tillerson spoke two or three days ago ... is that we do want to have a dialogue with them. We are open to dialogue and we hope that they will agree to have a dialogue ... he made it clear that we were open,  said Yun.  The U.S. delegation said in August it believed North Korean companies operated in Thailand and urged the Thais to shut them. In response, Thailand s foreign ministry told reporters that trade with North Korea had dropped by as much as 94 percent over the previous year. It did not give specific details. 