SEOUL, South Korea (AP) — South Korea's military says it's carefully monitoring North Korean nuclear and missile facilities after the country's spy agency told lawmakers that new activity was detected at a research center where the North presumably builds its long-range missiles targeting the U.S. mainland.

Seoul's Defense Ministry spokeswoman Choi Hyun-soo said Thursday the U.S. and South Korean militaries are maintaining close intelligence coordination over developments at the North's missile research center in Pyongyang and also a separate long-range rocket site. She did not elaborate what the developments were.

But a lawmaker says Seoul's spy chief in a closed-door intelligence briefing said increased vehicle movement was spotted at the Pyongyang facility.

The North conducted three flight tests of developmental intercontinental ballistic missiles in 2017 that demonstrated potential capability to reach the continental United States.