Report: S. Korea, U.S. consider their own sanctions against N. Korea SEOUL, Jan. 23 (UPI) -- South Korea and the United States may impose their own sanctions on North Korea for its rocket firing, a South Korean source told Yonhap News Wednesday. Quoting a senior South Korean diplomat, Yonhap reported such separate sanctions would be discussed at Thursday's meeting in Seoul between Glyn Davies, U.S. special representative for North Korea Policy, and Lim Sung-nam, South Korea's chief nuclear envoy. Any such move would come in addition to the tightening of existing sanctions related to a resolution approved Tuesday by the 15-member U.N. Security Council in response to North Korea's Dec. 12 rocket launch in defiance of earlier resolutions over the Communist country's missile and two nuclear tests. "We have been in discussions with the U.S. side about additional bilateral sanctions against the North following the U.N. resolution," the diplomat told Yonhap. They would make it harder for North Korean ships to navigate in the waters off the Korean Peninsula and tighten inspections of North Korean ships suspected of trafficking in weapons. The source said South Korea also is "in negotiations with other relevant countries" about similar bilateral sanctions. Immediately after the U.N. Security Council action, North Korea threatened to strengthen its "nuclear deterrence." There have already been reports the North may be preparing for a third nuclear test following its Dec. 12 rocket launch, which was seen by other nations as a cover to test its inter-continental ballistic missile capability. Separately, Yonhap quoted South Korean military officials as saying they have stepped up monitoring tunnels at North Korea's test site in light of the latest threat. Intelligence officials have been studying satellite images showing excavations and related movement at the Punggye-ri test site, Yonhap said. They said while the North may be ready to detonate a device on a few days' notice, the final decision would be made at political level.