North Korea helped Syria build an underground nuclear reactor in the Middle East country, a South Korean news report said Monday. "The US government has circumstantial (evidence) that the North provided technology assistance to build an underground reactor in Syria," South Korea's Hankook Ilbo newspaper reported, citing an unidentified diplomatic channel. US Embassy officials in Seoul were not immediately available for comment on the report. North Korea has repeatedly dismissed its alleged nuclear connection with Syria, saying that it had already pledged it would never transfer any nuclear material or technology out of the country. Monday's report came as the international process aimed at stripping North Korea of its nuclear weapons programs was at a deadlock over Pyongyang's refusal to give a complete list of its nuclear programs as required by a landmark agreement. US Assistant Secretary of State Christopher Hill arrived in Beijing earlier Monday for talks with Chinese officials on how to jump-start the stalled disarmament deal with North Korea. The US nuclear envoy was scheduled to visit Seoul and Tokyo this week for similar consultations.