A third U.S. Navy aircraft carrier strike group entered the western Pacific, the Navy announced Wednesday, just days ahead of President Donald Trump’s first trip to Asia next month.

The USS Nimitz joined the Roosevelt and Reagan in the region. The Nimitz announcement came a day after the Roosevelt entered the western Pacific.

The deployments came as U.S., Japanese and South Korean maritime forces were conducting a trilateral exercise aimed at improving ballistic missile defenses.

On Monday, Japan's defense minister asserted that North Korea's nuclear and ballistic missile capabilities had grown to an "unprecedented, critical and imminent" level, requiring "different responses."

The minister, Itsunori Onodera, said the rising threat compels his country to endorse the U.S. view that "all options" must be considered, which Trump has said includes possible military action. Japan was alarmed by North Korea twice launching ballistic missiles over Japanese territory, in August and in September.

U.S. Defense Secretary Jim Mattis slammed Pyongyang for defying U.N. Security Council resolutions against its nuclear and ballistic missile programs.

"North Korea's provocations threaten regional and global security," he said.

Fox News' Lucas Tomlinson contributed to this report.