North Korea made preparations for a nuclear test during the first six months of this year, according to an excerpt of a confidential United Nations report.

"Work at the Punggye-ri nuclear test site paves the way for additional nuclear tests for the development of nuclear weapons," independent sanctions monitors reported to the U.N. Security Council North Korea sanctions committee.

"The DPRK continued to develop its capability for the production of fissile material at the Yongbyon site," the monitors wrote, referring to North Korea's formal name — the Democratic People's Republic of Korea. Yongbyon is North Korea's major nuclear facility, operating its first nuclear reactors.