UNITED NATIONS (Reuters) - Russia accused the United States of denying entry to a senior military official to conduct a joint Russian and Chinese briefing at the United Nations on Thursday that criticized U.S. missile defense systems as a global threat. U.S. Disarmament Ambassador Robert Wood and Jeffrey Eberhardt, of the State Department Office of Multilateral and Nuclear Affairs, walked out of the briefing within minutes of it starting in a conference room at U.N. headquarters in New York. Alexander Emelianov, from the Russian Defense Ministry international cooperation committee, said Moscow had wanted to send a delegation led by Lieutenant General Tretyak Andrey, Russian Armed Forces chief of the General Staff Advisers Group.  The entry visa was not given to them,  Emelianov told the few dozen diplomats attending the half-hour briefing.  The U.S. mission to the United Nations declined to comment on individual visa cases or the Russian and Chinese briefing.  Russia and China have long been critical of U.S. missile defense systems, particularly the deployment of the Terminal High Altitude Area Defense (THAAD) in South Korea amid heightened tensions with North Korea over its ballistic missile and nuclear tests.   The Russian Federation is confident that the unlimited deployment of the U.S. anti-missile defense is a serious threat to the global security and can further unleash the arms race and threaten the entire humanity,  Emelianov told the briefing.  Major General Zhou Shangping, deputy director-general of the Operations Bureau, the Joint Staff Department of the Central Military Commission, also briefed.   The deployment of the THAAD system does little to upgrade the surveillance capability against the DPRK (North Korea), but significantly enhances the capability to monitor China s strategic depth and Russia s Far East,  Zhou said.  China and Russia have repeatedly demanded the United States halt the deployment of THAAD in South Korea. 